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UNIVERSITY OF ILLINOIS BULLETIN 

Vol. 4. MARCH 1, 1907 No. 13 

[Entered at Urbana, Illinois, as second-class matter] 



STUDIES FROM THE SCHOOL OF CERAMICS 

NUMBER THREE. 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR 
OF CLAYS 



BY 



R. C. PURDY AND J. K. MOORE. 



PUBLISHED FORTNIGHTLY BY THE UNIVERSITY 



[Reprinted from the Transactions of tub Ambkican Ceramic Society, Vol. IX. Paper 
read at St. Louit meeting, February, 1907.] 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR 
OF CLAYS 

BY 

Ross C. PURDY AND JOSEPH K. MOORE^ 

Champaigu, Ills. 

INTRODUCTION. 

The v.'ork of Orton and Griffin on the "Effect of Car- 
bon in the Burning of Clay Wares," Orton on the "Role of 
Iron in Clays," Kennedy on the "Dehydration of Clay and 
Decarbonization of Calcium Carbonate," Singer on the 
"Decarbonization of Ferrous Carbonate," and Lovejoy on 
the "Expansion of Brick during Water-smoking," etc., are 
some of the studies of the pyro-chemical and physical be- 
havior of clays that have been reported in the Transactions 
of the American Ceramic Society. Considerable attention 
also has been given to similar studies by our contemporar- 
ies in the English Ceramic Society during the past three or 
four years. Time and space will not permit of a review of 
these studies, nor of the man}- observations that have been 
reported in the trade periodicals since ceramics has been 
classed as a science. 

Since in every clay industry it is in the burning that 
the usefulness of a clay is developed, the burning properties 
may justly be considered the most essential or vital factors 
to be studied, A clay may lend itself readily to manufac- 
turing processes, and yet not develop in burning the pro- 
perties requisite for making it into serviceable ware. Claj» 
may differ widely in chemical, mineralogical, and physical' 
constitution and yet be equally valuable for manufacture- 
into a given product. 

In clay burning, the combined influence of the chemi- 
cal, mineralogical and physical properties of clay consti- 
tute the cause, and the pyro-chemioal and physical proppT- 

p. & .M.— 1. Q 



/\. 



4 PYRO-CHEMICAIi AND PHYSICAI. BEHAVIOK OF CLAYS. 

ties constitute the effects; knowing the causes, the effect 
ought to be interpretable. Owing, however, to the complex 
composition of clay and the variable properties of its sev- 
eral constituent parts, the true causes cannot all be ascer- 
tained in a sufficiently short time to justify the labor, even 
if methods were known by which they could be obtained. 
The effects, however, can be readily observed. 

Classification of clays on either the geological or the 
industrial basis has been attempted by many of the fore- 
most ceramic thinkers, yet it is freely admitted that as yet 
no satisfactory arrangement has been suggested. There is 
no agreement between the commercial value of clays and 
their geological age. 

Clays from which first class paving brick can be manu- 
factured, for instance, can be found in strata of any age 
and under almost any geological condition. Fire clays and 
shales of all ages are being successfully used in the manu- 
facture of paving brick. Glacial and alluvial deposits of 
clays have been found that are likewise serviceable for this 
purpose. Because the chances are far better of finding 
clays that can be made into paving brick among the fossil 
clays, the prevalent opinion is that it is to these types that 
paving brick manufacturers must look for their material. 
The facts are that there are many shales that are not fit to 
be manufactured into common building brick, much less 
into paving brick. Geological age or distribution, there- 
fore, has proven an unsatisfactory basis of classification. 

Chemical analyses of clays have been used in some 
cases as a basis of classification, but so unsatisfactory were 
the results that but very little importance can be attached 
to such a classification. 

A classification of the clays lying within political or 
natural boundaries, using as a basis the properties that 
are most essential to adapt each class to its commercial 
uses, has been the object of extensive researches of the 
United States Geological Survey and the various State 
Geological Surveys. Descriptions of the location and pro- 
perties of the clays to be found in the several survey re- 



PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 5 

ports have failed in this respect. In some Survey reports, 
notably those of Iowa and West Virginia, a few of the pyro- 
chemical properties of their clays have been described, but 
in no case has much significance been attached to their 
determination. In fact, in no case has the study of the 
pyro-chemical properties been carried to such a degree of 
completeness as would warrant very conclusive deductions. 
Having had opportunity to study the clays of Illinois, un- 
der the direction of the Geological Survey of that State, 
the writers, after nearly three months of research, came to 
recognize their inability to draw satisfactory conclusions 
from the several tests made of the properties of raw clays, 
and to appreciate the importance of a more exhaustive 
study of the chemical and physical changes that occur dur- 
ing the progress of burning from dehydration and oxida- 
tion to fusion. 

Believing that a study of the changes in porosity and 
specific gravity at successively increasing heats affords a 
practical method for testing and classifying clays, and also 
a method that makes possible in most cases an accurate 
estimate of the commercial possibilities of a given class or 
type of clay, and further being confident that this method 
makes it possible to determine the most important proper- 
ties of any clay, we present here a detailed account of the 
way in which our tests were made and a few of the results 
of our investigations. 

SAMPLES OF CLAY INVESTIGATED. 

Location and condition : Clays used by the more im- 
portant paving brick factories of Ohio, Indiana, Illinois, 
Missouri, and Kansas were obtained in what was termed 
"dry-pan samples," i. e. they were taken from the chutes 
leading to the pug mill, after having been pulverized in the 
dry pans. Clays collected from several parts of Illinois 
and not used in the manufacture of ware at the place of 
sampling, were ground in a five-foot dry-pan in the labora- 
tories of the Ceramic Department of the University of 
Illinois. 



6 PYKO-CIIEMICAL AKD PHYSICAL BEHAVIOR OF CLAYS. 

Types: Fire clays, shales and loess were the types 
of clays tested. There was not a sufficient variety of types 
nor enough samples of each type on hand to make an ex- 
haustive study, but this lack of samples does not lessen 
to any great extent the value of the results obtained. 

MANUFACTURE OF TEST PIECES. 

Wedging : Approximately one pound of dry clay was 
placed on a dampened plaster-covered table and sufficient 
water from the city mains added to develop the plasticity 
required to permit batting the clay into loaves. This was 
accomplished by adding the water in small quantities, and 
thoroughly working it into the clay each time, until the 
mass had the desired plasticity. It was then thoroughly 
wedged by kneading and batting until, on cutting the mass 
open, it appeared to be compact, i. e. without air blebs. 

Moulding : The loaf was then subdivided into smaller 
portions, each just sufficient to fill a mould 3/, inch x 21,4 
inches x 4i^ inches. The slabs were made to fill the mould 
by pressure applied in a screw press. They were then 
placed in a miter-box and cut into brickettes % inch x % 
inch x 214 inches. 

Marking : The laboratory sample number and a serial 
number was stamped on each brickette. 

Drying: The brickettes were dried in an open room 
at summer heat. It had been found possible to dry even 
the most tender of clays in this manner, so it was assumed 
that all clays used in this test could, without detriment, be 
subjected to this treatment. 

Burning: Twenty-four brickettes of each clay were 
prepared. The ones on which the serial numbers 1 and 2 
had been stamped were placed in a saggar to be drawn at 
Cone 010, those on which the serial numbers 3 and 4 were 
stamped were placed in a saggar to be drawn at Cone 08 
and so on — each successive pair of brickettes of each clay 
being placed in a saggar to be drawn at a predetermined 
heat as follows : 



PYRO-CHEMIOAL AND PHYSICAIi BEHAVIOK OF CLAYS. 



Series No. ou 1 
brickette | 


Heat at which 
drawn 


Hours intervening between 
draws 






Oxidized at 800 for 2 


1, 2 


010 


hours. From 800°C to 
cone 010 6 hours. 


3, 4 


08 


2 hours 


5, 6 


06 


2 hours 


7. 8 


04 


2 hours 


9,10 


02 


2 hours 


11,12 


1 


2 hours 


13,14 


3 


2 hours 


15,16 


5 


2 hours 


17,18 


7 


2 hours 


19,20 


9 


2 hours 


21,22 


11 


2 hours 



\ 



The bric'kettes in the saggars to be fired from cones 3 
to 11 were packed loosely in coarse white placing-sand, so 
as to prevent their sticking one to another. Only those 
clays known to be fire clays, or at least sufficiently refrac- 
tory to withstand severe heat treatment were placed in the 
saggars to be drawn at the higher cones. 

The eleven saggars were placed in a coke-fired, side- 
down-draft kiln in a manner convenient for drawing. The 
"spy" cones were centrally located in the kiln in a shield 
that protected them at all times from direct contact with 
the flame. When cone 010 was bent over sufficiently to 
touch the placque, the wicket was opened enough to draw 
the cone 010 saggar, the wicket replaced, and the heat 
slowly raised as shown in the above table. 

Cooling: The saggars in which the brickettes were 
placed were "tile setters'' 2 inches deep and 8 inches x 8 
inches in area. Before placing another saggar was in- 
verted over the one containing the brickettes, so that on 
drawing, the brickettes were at no time exposed to the re- 
latively cold temperature of the room, except in one case 
of accident. The saggars were placed, uncovered, in the 
ash pit of the kiln, where tliey were exposed to the direct 
radiation from the hot grate bars above. In this manner, 
the brickettes were cooled rapidly at first, thus preventing 



8 PYKO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 

the fused portions in the briekettes from crystallizing very 
much, but from dull redness down to blackness the cooling 
extended over a considerable period. 

The method of cooling pursued in this investigation 
was not ideal. The briekettes should have been cooled 
slowly for the first 200 °C which, as above stated, was not 
the case. Inasmuch as there is danger of checking the 
vitrified briekettes by cooling down to room temperature 
too rapidly, some attention should be given to the last as 
well as to the first stage of the cooling period, but more 
particularly to the first. It was not possible to cool the 
briekettes under these ideal conditions, for the services of 
the kiln were in demand for other purposes, and circum- 
stances did not permit of delaying the burning until such 
times as the kiln would not be in use. 

Preparwg briekettes for testing: When cooled, sand 
grains were found to be fused to many of the briekettes, 
requiring that they be ground off on an emery wheel. Care 
was taken not to unduly heat the bricks while grinding off 
the sand, and yet as little water as possible was used. The 
bricks that were thus ground were washed in distilled 
water to remove all traces of dirt and adhering particles. 
From the unground briekettes all adhering particles were 
removed by a dry stiff brush. Each brickette was carefully 
examined for flaws induced during manufacture or cooling, 
and also in order to remove all adhering portions such as 
broken corners that might have been detached later in the 
test. 

Up to this point, all briekettes were handled together, 
without regard to sample or series number, except as before 
indicated. 

TESTING OP BRICKETTES. 

In all, 60 clays w^ere prepared for testing as above de- 
scribed, using 16 to 22 briekettes for each. The briekettes 
were now sorted, those of each clay being treated as a unit, 
so as to insure like conditions at all times for all briekettes 
of the same clay. 



PYKO-CHEMICAl, AND PHYSICAL BEHAVIOR OF CLAYS. 9 

Drying of Brickettes : Brickettes belonging to two or 
three clays were placed in a drying oven and dried at 
240^C. At the expiration of four hours at this t(MU]H'rature, 
they were cooled in desicators preparatory to obtaining the 
dry weight of each brickette. 

Dry Weights : The dry weight of each brickette was 
found to the third decimal place on a chemical balance. 

Saturation of Brickettes : After the dry weights had 
been obtained, the brickettes were placed in aluminum 
pans, keeping them arranged in the pans in their regular 
serial order. Distilled water was added until only the 
npper surface of each test piece was above the level of the 
water. This exposure of one face of the brickette was to 
permit easy escape of the air from the interior of the brick, 
as it was being displaced by the distilled water. After 
standing thus in water for 18 to 24 hours, they were 
completely immersed. 

After a total of 48 hours in water, the brickettes were 
placed in water under a bell jar, and the air exhanste<l. In 
nearly every case, when a partial vacuum had been created, 
the air escaped from the brickettes at such a rate and in 
such volumes as to cause the water to appear to be boiling. 
From a previous experiment, the data of which are given 
in the following table, it was thought that in the average 
case, fairly complete saturation could be attained with 15 
minutes treatment in a partial vacuum. 



10 



PYBO-CHBMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 



TABLE I. 
Showing efficiency of vacuum treatment in affecting saturation. 



Sample 


Porosity as 
determined 
after 48 hrs. 
saturation 
without air 
exhaustion. 


Precentage of gain in porosity at conclusion of 
vacuum treatment extending over period of 




5 min. | 


10 mln. 1 15 min. | 


20 min. 


S 2 


3.22 


48.1 


51.8 


57.9 


65.0 


G II 


3.3 


38.7 


42.1 


48.4 


50.6 


K 4b 


3.93 


27.3 




35.6 


37.5 


K 15d 


4.22 


13.48 


14.48 


18.7 


20.8 


K 13c 


4.27 


44.60 


46.60 


46.6 


46.6 


K 15c 


4.51 


33.40 


36.50 


36.8 


38.2 


R 4 


5.12 


58.2 


59.4 


61.7 


63.7 


H II 


5.29 


31.2 


35.4 


37.6 


38.9 


R 2 


6.1 


27.5 


32.2 


35.6 


36.0 


K 6(1 


6.4G 


29.9 


31.6 


35.3 


39.3 


K 2 


6.55 


18.6 


20.1 


21.6 


24.3 


R 1 


6.7 


10.2 


11.0 


11.0 


11.0 


B II 


6.91 


28.0 


30.4 


31.4 


32.0 


J II 


7.53 


11.8 


13.7 


15.7 


16.0 


I IT 


8.64 


11.8 


12.8 


14.1 


14.8 


K 8d 


9.06 


22.0 


23.5 


24.0 


24.9 


B I 


9.39 


13.11 


20.3 


23.4 




K 15b 


19.8 


6.05 


6.22 


6.84 


7.34 



Wet and Suspended Weights: Each saturated brick- 
ette was in turn suspended by a silk thread from the beam 
of a chemical balance, and its saturated weight taken, al- 
lowing for the weight of the thread. Without removal from 
the balance, a glass of water was placed on a bridge span- 
ning the scale pan in such a manner as to cause the brick- 
ette to swing absolutely free but completely immersed in 
the water. The suspended weight of the brickette was 
thus taken. 

Calculations : The percentage of porosity of each 
brickette was calculated bv the formula : 



Percentage of Porositj^ = 



' Wet Weiglit, — Dry Weight \ , ^^ 
, Wet Weight — Suspended Weight/ 



This expression for percentage of porosity is, so far as 
is known to the writers, here first presented. It is a sim- 
plified form of the follov.ing expression, whicli is given in 



PYRO-OHEMTCAIi AND PHYSICAL BEHAVIOR OF CLAYS. 11 

Dearly all of the Reports of Geological Surveys on Clays, 
in which this method of obtaining porosity has been used. 

/ [W— D] Sp. Gr. \ 
Percentage of Porosity = ( [W— D] Sp. Gr.+D ) ^^ 

In this latter expression for percentage of porosity, 
\V=wet weight; D=Dry weight. By substituting for the 
last D in the denominator its value obtained from the ex- 
pression for specific gravity: 

/ Dry Weight \ 

Sp. Gr.=^^ jjj^ Weight— Suspeuded~Weight / 

or, D = D X Sp. Gr.— S X Sp. Gr 

Where S=Suspended weight, the expression reduces 



to 



/ WXSp. Gr.— DxSp. Gr. 

lOOf ^ 



,WXSp. Gr.— DxSp. Gr.+ DxSp. Gr - S x Sp 



5p. Gr } 



By canceling "Sp. Gr." and collecting terms, the sim- 
plified formula for percentage of porosity first given is 
deduced. 

Plotting of Results: In a previous study of similar 
character to the one here reported, the writers had arbi- 
trarily established the following proportion : Linear 
length on ordinate, equal to 1% porosity: linear length on 
abscissa equal to difference of heat treatment of one 
cone : :1 :1. This was maintained between the coordinate 
factors of the porositygraphs, so that the rate of decrease 
in porosity could be expressed numerically in terms of the 
taiir;oncy or slope of the curves, and that the factors so 
obtained would be comparable one with another at all 
times. 

The divisions on the abscissas of the specific gravity 
curves are the same as those of the porosity curves. The 
divisions on the ordinate are proportionally; 0.1 Sp. Gr. : 1 
cone heat ::!:!. 



12 PYBO-OHEMICAL AND PHYSICAIi BEHAVIOR OP CLAYS. 

PYRO-PHYSICAL-CHEMICAL BEHAVIOR OF CLAYS. 

The physical-chemical changes that take place in burn- 
ing may be discussed under three headings : 

1 Water-smoking. 

2 Dehydration and Oxidation. 

3 Fusion. 

Water Smoking : During the water-smoking or driv- 
ing off of the mechanical and hygroscopic water, clay wares 
expand, as is shown by Mr. Lovejoy's settling curves.^ 

This would scarcely be a noteworthy physical change, 
were it not for the fact that clays either expand again or 
retain their expanded form through water smoking to the 
completion of the oxidation and dehydration period. The 
writers' experiments have shown that this physical change 
differs in character and intensity with different clays, but 
their work is not sufficiently detailed and accurate to for- 
mulate data or draw conclusion further than that with 
some clays this transition period from water-smoking to 
oxidation is somewhat critical. 

Deliydration and OxidaUo7i : The majority of clays 
are dehydrated completely when subjected to heat at 500°- 
600 °C, others are not. Tn nearly all fossil clays, dehydra- 
tion precedes oxidation, while in a few instances the re- 
verse is true, as will be noted later. 

It is unnecessary to describe in detail the various 
chemical changes that occur during this period of the burn- 
ing, for the alterations in the iron'-' coniponnds and the ox- 
idation of the carbon^ have been very exhaustively con- 
sidered by Orton. 

Notable exceptions to the usual behavior during dehy- 
dration and oxidation were observed in the study of the 
Illinois clays: 

First. K 14, a mined shale, slaked down to a plastic 
mass after being subjected to a heat treatment which aver- 
aged about 625° C for 16 hours, as shown in the following 
curve : 

iTrans. Am. Cer. Soc. Vol. VII, p 422. 

2Ibi(i. Vol. V, p 377. 

^Second Report, Com. on Tech. Inves., Natl Brick Mfg. Assoc. 



PYBO-OHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 



13 





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11 PYBO-CHEMICAIi AND PHYSICAL BEHAVIOR OF CLAYS, 

The shale oxidized easily and before it was com- 
pletely dehydrated. Six other clays exhibited a reversal of 
the usual oxidization and dehydration changes, but none 
in so pronounced a degree as in the case of K 14. 

As yet no data have been obtained concerning the 
chemical or physical constitution of these clays that will 
shed light upon these rather remarkable exceptions to the 
usual order in which the dehydration and oxidation take 
place. The fact is established, however, that the cases are 
not rare where both changes take place simultaneously, 
and in a few cases the usual order is reversed. 

Second. In the case of H 23, oxidation had not pro- 
gressed very far at the end of 24 hours exposure at 650°, 
and the unoxidized portion of the brickettes vitrified on 
further heating to as hard and dense a mass as did the 
outer oxidized portions. No swelling or distortion of the 
brick due to the oxidation of the carbon and ferrous iron 
was noted. In fact, the shrinkage and rate of decrease in 
porosity was not abnormal in any respect. In figure 2, are 
shown the volume-shrinkage, porosity, and specific gravity 
curves for this clay. (See page 216.) 

In this figure, the specific gravity, porosity and volume 
of the bricks burned at different temperatures are calcu- 
lated in terms of the percentage of increase or decrease 
over those of the unburnt bricks. In other words, the raw 
factors are considered as a basis or datum from which the 
"burned" factors are calculated as increase or decrease. 
Zero or the datum line, therefore, represents the data ob- 
tained from the unburnt bricks. 

The percentage of increase of the burnt ware over that 
of the unburnt is shown above the datum line on the ordi- 
nate, and the percentage of decrease is shown below the 
datum line. On the abscissae is shown the actual percent- 
age of porosity of the burned brick. 

Points on the same ordinate represent a single brick. 
We have not plotted the data from all the bricks studied 
in this test, but only those in which the percentage of por- 



PYBO-CHEMICAIj and physical behavior of CLAYS- 



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16 PYRO-CHEMICAL AND PHYSIC AIj BEHAVrOB OF CLAYS. 

osity differed sufficiently to fix points on the curves that 
would show a comparative increase or decrease in the sev- 
eral factors. 

The fact that the actual percentage of porosity of the 
burned brick was taken in each case as a point on the ab- 
scissa, without regard to the porosity of the unburiit brick, 
will account of the irregularity in the curves. 

Notwithstanding the fact that the black unoxidized 
core remained, even when the whole exhibited a porosity 
of only 2%, the brick continued to shrink normally with 
each increase of temperature, and the specific gravity of 
the brick decreased less than in the case of many normally 
burned paving brick shales. This steady decrease in vol- 
ume and comparatively slight decrease in specific gravity 
gives evidence of a thermo-physical behavior that is oppo- 
site to that of the majority of clays containing carbon. 

(See plate III, facing page 218.) 

PHYSICAL CHANGES DURING OXIDATION AND DEHYDRATION. 

Contrary to the statements usually made concerning 
the physical changes in a brick at this period, our investi- 
gations show positively that not only the porosity, but also 
the volume and specific gravity of the brick are increased, 
and that it is indeed an exceptional case where all of these 
factors are not larger during the time of oxidation and 
dehydration than they were in the unburnt condition. 

A most peculiar and noteworthy fact in this connec- 
tion is that in many cases the specific gravity and volume 
remain large until the porosity has been increased to that 
of the unburnt brick. 

FUSION. 

From the laws of physical chemistry, it could not be 
expected that the heterogeneous mineral mass called clay, 
consisting largely of amorphous materials, would have a 
definite fusion point. According to Walker^ this would 
more properly be called a fusion period. 

'Introduction to Physical Chemistry, p. 64. 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 17 

Our studies, a part of the data of which are shown in 
subsequent curves, bear out this statement. It will be seen 
that in the case of the purest clays, according to the specific 
gravity curves, fusion begins as early as cone 3. In the 
case of some of the most impure shales, high in lime, fusion 
begins at a period considerably earlier than cone 010, 
Fusion thus early begun progresses with more or less regu- 
larity until the whole mass enters into the active thermo- 
chemical reaction and deformation of the ware ensues. 
Incipient vitrification, vitrification, and like terms are only 
descriptive of the effects at different stages of fusion. It is 
the rate of fusion, therefore, that determines the pyro- 
physical effects produced in the burning of clay wares dur- 
ing this period. The factors affecting rate of fusion are : 
The factors affecting rate of fusion are : 

1st. Mineralogical composition. 

2nd. Size of grain. 

3rd. Volatile matter. 

4th. Adsorbed salts. 

MINERALOGICAL COMPOSITIOxN. 

Synthetical studies of fusions of mixtures of pure 
minerals, have shown that the same chemical elements, 
brought together as constituent parts of different minerals, 
produce mixtures having unlike fusion periods. The rate 
of fusion and the regularity with which it progresses, as 
well as the point of complete yielding, are affected very 
largely by the manner in which the various elements are 
previously combined. Because of the difficulty of making a 
microscopic mineralogical analysis of a clay, the knowl- 
edge of these facts cannot aid in an attempt to foretell or 
explain in full the fusing behavior of clays. Realization, 
therefore, of the fact that difference in mineralogical make- 
up of clays of like ultimate chemical constitution causes 
difference in their fusion behavior is the only result of 
practical value that has so far come from the study of the 
fusion behavior of synthetical mixtures of minerals. 



18 PYBO-CHEMICAL AND I'HYSICAJj BEHAVIOR OF CLAYS. 

There is one yerj notable exception to the above, and 
that is in the case of calcium carbonate. The effect of cal- 
cium carbonate depending upon the size of the grain and 
extent and homogeneity of diffusion throughout the clay 
mass, operates in a two-fold manner. If thoroughly 
blended with the clay in small particles, it operates as a 
very active flux. Its fluxing effect is most notable on ac- 
count of the rapidity with which the thermo-chemical re- 
actions between the nascent oxide and clay takes place. 
This reaction is in some instances so rapid as to make it 
very dangerous to approach the vitrification temperature. 
If the calcium carbonate is present in nodules, the thermo- 
chemical reaction just described can take place only at the 
points of contact of the decarbonized lime and clay, the 
remainder of the carbonate being converted into quick lime. 
The different effects of lime in these two physical condi- 
tions on the rate and regularity of fusion of the clay mass 
is obvious. 

SIZE OF GRAIN. 

The full significance of this factor can be appreciated 
only by considering extreme cases, as in the case of cal- 
cium carbonate, above cited, or as in a mixture of two min- 
erals such as feldspar and flint. When feldspar and flint 
are mixed as fine powders in the proportion of 75% feld- 
spar and 25% flint, the mass will be fused to a fluid at ap- 
proximately 1100° C in a comparatively short time. If, 
however, these two minerals were placed side by side in the 
shape of rectangular pieces having the same proportional 
weight as in the first case, the only fluxing action that 
would take place at 1100°C would be at the points of con- 
tact. Even if the heat was held at 1100° C, complete fusion 
of the two piecs of mineral could only take place when the 
glass, formed at the point of contact, enveloped and slowly 
ate into the unfused portions, and thus produced an inti- 
mate mixture of the two minerals by diffusion or surface 
tension. It is common experience that if complete fusion of 
the two minerals at 1100° C is desired when brought togeth- 



' «f -^.- ^'"- ?y> 




1 



1 



I -I 



<^ 



Pi.ATE III. Sli(>win<r ;i brick which xinilor-wenf noniial c-lianj^es 
ill (Icn-iiry. siH'cifi<- gravity and s!irinka.<;e. in s])ifc of hl;Hk«Miiii.<? due to 
iiiil>err('ir uxydatiim. 



PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 19 

er in the form of coarse particles, considerable time must be 
allowed, and that to effect complete fusion in a shorter 
time, the heat must be raised from 1100°C to 1230'^ (ap- 
proximately) or the fusing point of feldspar. At this tem- 
perature, the feldspar melting would completely envelope 
or perhaps float the flint particles, and slowly attack and 
dissolve them away, just as water will attack and dissolve 
away a piece of loaf sugar. 

The above illustration, while an exaggerated case, 
nevertheless is descriptive of the effect of fineness of grain 
on the fusion of any two minerals that have thermal reac- 
tions one with another, and also descriptive of the fusion 
of a mixture containing particles of several minerals as a 
clay. 

In the burning of clay wares, where time is an import- 
ant and unavoidable factor, the effect of fineness of grain 
influencing the fusing of clays is particularly noteworthy. 
By the manufacturers of pyrometric cones it has been re- 
cognized as being such a powerful factor that the utmost 
care is taken to maintain uniformity in size of grain in 
their materials, both before and after manufacture into 
powdered cone stock. The importance of the time factor 
has been emphasized in ceramic literature so often as to 
render further remarks on this point unnecessary. 

VOL-\TILE MATTER. 

Chemically combined water, carbonic acid gas, carbon, 
etc., do not of themselves, on expulsion, cause thermo- 
ehemical reactions to take place between the stable bases, 
acids and silicate compounds left behind, but their expul- 
sion does involve changes in physical and, in some sense, 
chemical conditions that provokes thermo-chemical reac- 
tions between the remaining substances. For example, in 
terra cotta lumber, sawdust is added, so that when it burns 
out, it leaves the mass extremely porous, i. e. not dense as it 
would otherwise have been. The sawdust in this instance 
has been effective in opening the structure of the ware and 

p. & M— 2. 



20 PYBO-CHEMICAL AND PHYSICAIj BEHAVIOR OF CLAYS. 

preventing the particles in the clay mass from coming with- 
in fluxing distance of one another as they otherwise would. 
What is true in the case of the sawdust in terra cotta lum- 
ber is true of combustible organic matter in clays. It is 
obvious, however, that the influence of carbon in this con- 
nection depends to a very large degree on the size of the 
carbon particles. 

The effect on the thermo-chemical behavior of clays 
of the expulsion of CO2 from such compounds as ferrous 
carbonate, calcium carbonate, etc., is another familiar phe- 
nomenon, the importance of which is not recognized in the 
attempt to interpret the results of an ultimate chemical 
analysis. If two equal portions of the same clay are taken, 
and to the one a quantity of red iron oxide (FeoOg) and to 
the other an equivalent quantity of powdered ferrous car- 
bonate (FeCOg) and the two mixtures burned under the 
same thermal conditions, it will be found that the mixture 
containing the ferrous carbonate will begin to fuse earlier, 
exhibit a more erratic rate of decrease in specific gravity 
as the intensity of the heat increases, and may or may not, 
depending upon conditions other than those here consid- 
ered, cause an earlier ultimate fusion. The same is true to 
a greater or less extent in the relative fluxing effect of the 
oxides and carbonates of other bases. 

The same phenomena are also notable in the compara- 
tive fluxing effect of such hydrous and anhydrous silicate 
compounds as raw and calcined kaolin. 

When one ingredient of a chemical compound is driven 
out by heat, or otherwise separated, the remaining portion 
is said to be in the nascent state, i. e. eager to combine with 
anything for which it has an affinity. If in an intimate 
mixture of clay and calcium carbonate, the clay is being 
dehydrated at the time the calcium carbonate is losing its 
COo, rapid fluxing between the two will ensue. In fact, 
dehydration of clay in the presence of calcium carbonate 
causes earlier expulsion of the carbonic acid gas from the 
carbonate. 



PYB()-CHBlrflCAIi AND I'HYSICAL BEHAVIOR OF CLAYS. 21 

ADSORBED SALTS. 

The iufluence of the adsorbed salts in a clay on its 
pyro-ehemical and physical changes are not very well un- 
derstood. In fact, little is known about adsorbed salts be- 
yond the fact that they are present in nearly all, if not all, 
plastic clays. A few thermal phenomena, however, are un- 
explainable except on the assumption that adsorbed salts 
are present in such forms and quantities that they may be 
considered as the cause of these phenomena. 

In the tirst place, assuming that it is the influence of 
adsorbed salts that gives to a clay its plasticity, (an ex- 
ceedingly probable assumption) the peculiar fact that 
sample K 14, before cited, could retain considerable plas- 
ticity even after subjection to a temperature of 625° C for 
16 hours may be explained by the possibility that some of 
the adsorbed salts had either not lost their peculiar proper- 
ties of giving to the clay grains a slipperiness which we call 
plasticity, or that they regained these properties by rehy- 
dration. The same may be said in regard to the plasticity 
developed in slate and hornblend by wet grinding. 

Further, the adsorbed salts may be volatilized at tem- 
peratures that are sufficient to cause the dehydration of 
clays. We know that considerable material can be volati- 
lized from clay by dry distillation, and it seems safe to as- 
sume that the material so volatilized was present in the 
clay as salts unstable at comparatively low temperatures. 
Hopwood^ has shown that the volatile material may po.s- 
sibly in some cases be silica or alumina. Dr. Kahlenlmrg 
in a lecture delivered at the University of Illinois reported 
the finding of a surprisingly large quantity of SiOo in the 
gases given off from fodder in Silos. In fact, sufficient 
evidence is at hand to warrant the assumption that the ad- 
sorbed salts of a clay may be of various composition, and 
need not necessarily be alkaline salts. Loss of plasticity 
due to the volatilization of the soluble salts before they 
have had opportunity to operate as fluxes therefore, is a 



'Trans. Eng. Cer. Soc, 1904-5, p. 37. 



22 PYRO-CHEMICAL AND PHYSICAL BEHAVIOK OF CLAYS. 

very probable fact. It is equally probable that there are 
some adsorbed salts which either are not volatile, or are 
so confined in the clay that they are not expelled on 
heating-. 

If any salt is thus retained on heating;, the clay can 
readily slake down in water to a mass, the plasticity of 
which is proportional to the amount of retained soluble salt 
and degree of delinquesence of the salt so retained. It is 
not uncommon to find soft burned brick and drain tile 
slaking down to a plastic mass. 

It is a fact, also, that the least plastic clays and conse- 
quently, according to the cause of plasticity assumed in 
these discussions, those containing the least amount of 
adsorbed salts, require higher heat to make a sound frost- 
resisting ware, and that in most cases tlie clays that can be 
burned into such ware at the lowest heats are very plastic. 
In the first of the cases, there is an absence of a fluxing 
medium between the grains and in the second case the salts 
at their melting heat fuse and cement the grains. 

If, however, all the salts have neither been volatilized 
nor fused, it may be that they are retained in a loose com- 
bination with the dehydrated silicate of alumina, which 
can be broken down under the influence of water, and both 
the salt and kaolin rehydrated. This assumption is believed 
to be substantiated by the fact that it was the brick made 
from clays whose so-called coarse grains were not indivi- 
dual crystals, but bunches of minute grains cemented to- 
gether by a salt that is but slightly soluble and hence re- 
sists disintegration in water even under long and severe 
treatment, that slaked after having been subjected to 625° G 
in the kiln. 

PRECIPITATED MATERIAL. 

Calcium carbonate, hydrates of silica, alumina, and 
iron, as well as zeolitic compounds, when first precipitated 
or formed, are in the majority of cases in extremely fine 
grains. The fluxing behavior of any substance is mater- 
ially different when thoroughly disseminated in minute 



PYRO-OHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 23 

grains, especially in the colloidal form, than when present 
in coarser grains. Iron, for instance, has been found to 
enter into chemical combination with silica as a ferric sili- 
cate when the iron is precipitated on flint and as a ferrous 
silicate, if at all, when the two are mixed as dry powders.^ 
The vast -difference between the fluxing action of ferrous 
and ferric oxides and compounds need not be discussed at 
this time. The important fact in this connection, however, 
is that it depends to a very large extent on the form and 
manner in which the iron is disseminated through the clay, 
as to whether it will combine as the lower or higher oxide. 
What is true of iron in this regard is true in a degree of 
other fluxes. 

SUMMARY OF FACTORS AFFECTING MANNER OF FUSION OF 

CLAYS. 

1st. The manner in which the several constituent ele- 
ments are combined, one with another, very materially af- 
fects the fluxing behavior of a clay. 

2nd. The size of grains of the several mineral con- 
stituents is an important factor in determining the fusing 
behavior of clays. 

3d. The amount, form, and character of the volatile 
constituents of clay does not directly affect the thermo- 
chemical reactions, but the difference in the physical con- 
dition, structure of the clay, and the stability of the non- 
volatilized compounds caused by the expulsion of these 
substances, does materially affect the manner in which 
fusion takes place. 

4th. The importance of the role that adsorbed salts 
play in the fusing behavior of clays is little appreciated. 
The evidence on the manner in which they operate is so 
indirect and circumstantial that definite statements or con- 
clusions are impossible. That they are important factors, 
however, there is no doubt. 

5th. Concerning precipitated materials, we have evi- 
dence from synthetical experiments that prove beyond a 

'Trans. Am. Cer. Society, Vol. VII. 



24 PYRO-CHEMICAL, AND PHYSICAL BP^HAVIOB OF CLAYS. 

doubt that they must be considered as most potent in af- 
fecting the fusion of clays. 

From the above remarks, it is evident that the writers 
have but little confidence in the efficacy of an ultimate 
analysis of a clay as a means of foretelling its burning pro- 
perties. The combination, size of grain of the several com- 
pounds, solubility, volatility, and dissemination of the 
several salts, and lastly the manner in which the uncom- 
bined oxides are introduced into the clay are omre effective 
factors that the total ultimate composition. 

THERMO-CHEMICAL AND PHYSICAL CHANGES DURING FUSION. 

It is indeed very difficult if not impossible to deter- 
mine what the actual thermo-chemical reactions really are, 
which take place in the fusion of the clay particles first 
between themselves, and secondly when the whole mass 
becomes a more or less homogeiieons glass. ^ By the aid of 
the microscope, as will be seen later, more can be told in 
this respect than by any other means. But the effect of 
thermo-chemical reactions, however, can be detected by the 
changes in porosity and specific gravity. Because of our 
present inability to ascertain in full the reactions that take 
place, it seems best to refer to the chemical phases of fusion 
as "changes" instead of "reactions." 

The greater portion of the constituents of our clays 
being mineral substances, many of which do not entirely 
lose their identity in the burning of clay wares, it is most 
natural that these should exhibit in nature the same 
changes when treated separately that they do when heated 
togetlier in clays. Roth^ gives the following description of 
the physical changes in minerals on melting: 

•Prof. G. Tamman, Sprechsaal No. 35, 1904, summarizing his stud- 
ies on silicates says, "The volume of the glass is, at the lowest tem- 
peratures, larger than that of crystals." Mellor, Vol. V, p. 78, discusses 
the volume changes in silicates and cites A. Laurent (Ann. Chim. Phys. 
(2) 66, 96, 1837; A. Brongniart, Traite des Arts Ceramiques, 1, 283, 720, 
3877) and G. Rose (Pogg., Ill, 123, 1890; A. S. Day and E. S. Sheperd, 
Am. Journ. Science, (4) 22, 262, 1906. Dr. E. Berdel (cited Vol. VII. 
p. 148 A. C. S. Trans.) describes similar physical changes in the heat- 
ing of ceramic materials and bodies. 

2Allgemeine und Chemische Geologie, Vol II, p. 52. 



Mineral 


Specific 
Gravity of 
the Crystal 


Spec. Grav. 

when melted 

to Glass 


Percent. 
Reduct'n in 
Spec. Grav 


1 

Rbmarks 


Quartz 


2.663 


2.228 


16.3 




Quartz 


2.65 


2.19 


17.3 


Average 


Olivine 


3.3813 

3.0719 

2.561 

2.5522 

2.58 


2.8571 

2.2405 

2.3512 

2.33551 

2.381 


15.6 

27.0 

8.1 

8.5 

7.6 




Mica 


Glass compact 


Adular 




Adular 


Glass full of fine bubbles 


Sanidine 


Glass full of fine bubbles 




and dark-colored. 


Orthoclase 


2.574 


2.328 


9.6 


Glass full of fine bubbles 


Orthoclase 


2.5883 


2.3073 


10.9 


Glass colorless 


Microcline 


2.5393 


2.3069 


9.1 


Glass, colorless 


Albite 


2.604 


2.041 


21.6 


Full of fine bub- 




bles; white glass 


Oligoclase 


2.C6 


2.258 


15.1 


Glass full of fine 

bubbles 


Ollgoclase 


2.6061 


2.3621 


9.1 


White glass; bub- 
bly 


Oligoclase 


2.6141 


2.1765 


16.7 


Glass full of bub- 
bles 


Labradorite 

Hornblende 


2.7333 
3.2159 


2.5673 
2.8256 


6.1 
12.2 


Gli'ss sliRhtly bubbly, 
with black and white 
portions 

Glass compact 


Augite 


3.2667 


2.8035 


14.2 


Glass compact 


Epidote 


3.409 


2.984 


12.5 


Red brown garnet. . 


3.90 


3.05 


20.5 


Green glass 


Lime-iron garnet . . 


3.838 


3.340 


25.6 




Granite 


2.680 


2.427 


12.9 


Green Glass; transparent 
strongly blebbed. 




Granite 


2.751 


2.496 


9.3 


Black Glass; opaque; 
strongly blebbed. 




Hornblende granite 


2.643 


2.478 


6.2 


Black Glass ; opaque ; 
strongly blebbed. 


Felsite porphyry... 


2.576 


2.301 


10.7 


Transparent very blebby 
difficult of fusion. 


Syenite 


2.710 


2.43 


10.3 


Glass homogeneous; dark 
colored. 




Quartz diorite 


2.667 


2.403 


9.8 


Glass homogeneous; 
dark colored. 


Diorite, quartz free 
Gabbro 


2.779 
3.100 


2.608 
2.664 


6.3 
14.2 


Black Glass ; opaque ; 

compact; somewhat 

difficult to fuse. 
Black opaque glais ; 

easily fusible. 





25 



26 PYRO-OHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 

The alterations in the minerals and rocks above cited 
are those induced when they are changed by melting, from a 
crystalline to an amorphous condition. Such complete 
changes as this cannot be permitted to take place in the 
burning of clay ware, and yet, as will be shown, the per- 
centage of decrease in specific gravity of many of our clays 
from the unburnt to the vitreous stage is greater than that 
given in the above data. This being true, it is evident that 
there are factors other than the alteration of minerals from 
the crystalline to the amorphous condition that affect de- 
crease in the specific gravity of clays. 

In the following table are given data which show the 
effect of heat on physical structure of brickettes made from 
various clavs: 





i 


. Black iron specks. 
Small black iron specks. 
. No iron specks. 




0> 


CD 
O 








0) 

> 
en 


03 
03 

W) 


03* 

o 

03 

c 

03 


swollen & self-glazed at cone 9 

, chocolate at cone 3 and black 

apparent swelling at cone 5 

t cone 6, black at cone 7 and 9. 

at 7 

black at cones 6, 7 and 9. Swol- 

at 9 

spongey at 9 and biack In color 

en at cone 7 


K 
- C 

n c 
5 ^ 

U rt 


CO 

o 

a> 

D. 
CQ 

o 

U 


03 

a 
o 

u 
o 

3 


CO 

p 

o 
_cS 

.Q 03 

o B 


OJ 

o 

(U 
G 
03 

C 

o 


03 

o 

c. 

03 

o 
o 


OJ 03 

« P. - 

goo 
S Z « 


a 

03 

S 

5 ^ 

o 

. c 
-a 3 


o 

03 

<D 
.3 

B 
a 
a 

C3 

O M 


3 
O 
ti 

X 

03 


Cm 
O — 

It 


o 
Z 


a 

S 
en 


Z g 


o 
Z 


z 

■d 


. 03 . fl 

T5 CS -O 01 


J .9 
•of 


C3 
13 


Oo ij.O0J30 ][| 


i 


a «: 






0) m 




Q/ 


(B 52 03 t- 


0) o 


Q) 


s^ S 4,£ «■= « UJ f 


3 _; = 


3 




n '-; 




fl 


fl r " 5 


fl 3 


a "3 


3 


PS 


^ -a X5 




3 '^ 


a> 


3 


2 ^5 g 


o o 


2 o 


O 




•" JS ti 


.« 


JS 


Oi O 


.a 


03 


^ H « "^ 

£ g 3 


03 O. 


? z 








J3 M .c 




OJ 


ro 


O 


03 


03 


03 


-^■C«Ot^ J^iiJ< V -^^ 




bC rt M 


cfl 


CTl 


3 


c;1 


3 


3 


3 


J3 


« T j: ^ " rt — 






















w3 Cx. -3 


Q 


C-c, 


CO 


fc 


m 


02 ffi CQ 


CQ 


CQ 


CQ 


Ck o C5 Q c/: oa 


». c i n 














CO 








CO 00 Ol iH 113 lO CO 


s°e--o 














<ji ■ • 








00 ■«»< 00 iH CO CO iH 


«seu2 














CO . . 








»o t- M* a> CO o 00 


«j(3 fc 














iH 








iH iH CO iH iH CO CO 


c 


>. 








lO 






CO O CO 




t- 


o 




E 


o 


0> <M CO 


Oi 


i-H 


CO 


CO 


t> 


CO -^ CO 


t- 


•^ 


CO 


CO • '^ tr- O "* CO 


M 


o 


O <0 CO 


t^ 


■<ti 


o 


tH 


rH 


^ CO CO 


>C3 


CO 


Tf 


CO • CO CO CO us lO 


M 

s 


CLi 


Cq M 1-1 


t-H 


rH 


T-l 


1-1 


i-i 












c ^^ 


00 










CO 


CO 










•SS^ 


CO CO c- 


tH 


M 


M 


00 


o 


CO CO CO 


OS 


CO 


CO 


O t- CO lfi> O CO o 


3 
J 


o 


US lO ■«*< 


■««< 


lO 


■* 


00 


r^ 


00 00 t- 


iH 


CO 


o 


CO a> o> a> o OS CO 














iH 


iH 


iH 


iH 


CO iH CO CO CO iH CO 


a o 


OS OS tH 


tH 


T-l 


^-1 


1—1 


a> 


r-t 1-1 1-1 


iH 


05 


^ 


Oi us 0> O) O) OS t^ 


s 


y^ 


i-C 


i-H 


tH 


tH 


1-( 




1-1 iH 1-1 


'"' 




iH 
















>. 














OS 


iH 


U5 


Irt 




c 


"u! 














CO 1-1 o> 


o 


CO 


CO 


Tfl CO OS 0> T*< CO OJ 


















O 05 o 


lO 


Ci 


CO 


t- -<*' O CO t- CO iH 


> 


Zh 














rH iH 






iH 


iH tH 


■sl^ 














iH U5 LO 


CO 


CO 

iH 


CO 


O t- t- t- iH t- t- 


"3 
E 


^S^ 














CO 00 -f 


t- 


■«J< 


Ttl 


U5 CO O CO 00 t- t- 














tH 








IH iH tH tH 


2 


s ° 

(5z 






lO t- lO 


lO 


CO 


ir; 


us OS lo us CO us CO 


(A 


•rf T^ in 


05 


00 


rf 


f 


iH 


rH lO <0 


t~- 


CO 


CO 


iH CO 00 ■* CO 00 iH 


C^J »H 


l-H 








c^ 


<:\ 




'"' 




tH 


E > fc, 


:iH 


Ec( 


> 


fc 


fc 


ai > fe 


El< 


^ 


> 


ti! UJ Ui tiJ tsj til W 
























09 C» 03 03 03 03 ca 
























03 03 0) © 0) 03 a> 




















































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j3 ja J5 .a x3 .3 ja 


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28 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYg. 29 

It was a surprise to learn that bricks will decrease in 
volume without loss of weight, and at the same time de- 
crease in specific gravity. Had the clay been carried to 
complete fusion, i. e. to a ghiss, the decrease in specific 
gravity would have been credited to the same phenomenon 
as in the case of minerals, i, e. the changing of its consti- 
tuents from crystalline to amorphous forms. But in the 
case of a clay brickette, a very small portion of which con- 
sists of crystalline substances, decreasing in specific grav- 
ity before the minerals have been rendered amorphous, i. e. 
fused to a glass or even before vitrification has been com- 
pleted, can not be explained wholly on this basis. Mr. 
Wegemann, of the Geological Department was, therefore, 
requested to make a microscopic study of brickettes of two 
different clays burned at different temperatures, and his 
report follows: 



30 PYBO-CHEMICAI. AND PHYSICAL BEHAVIOR OF CLAYS. 

NOTES ON THE MICROSCOPIC STRUCTURE OP 

CERTAIN PAVING BRICK CLAYS, AT VARIOUS 

STAGES OF FUSION. 

In the hope of explaining some of the phenomena of 
simultaneous decrease in volume, porosity and specific 
gravity without loss in weight, and to obtain some idea of 
the manner in which fusion takes place in a vitrifying 
brick, microscopic sections were prepared from brickettes 
of two paving brick clays manufactured and burned by 
^Messrs Purdy and Moore in the manner described by them. 

Thin sections of brickettes burned at a low tempera- 
ture exhibit under the microscope a very fine-grained frag- 
mental ground mass, or matrix, in which are imbedded 
crystalline and other fragments, which were present in the 
original clay. From these materials are developed at high 
temperatures amorphous glass and crystals. 

The cavities betvreen the particles of a brick may be 
divided into two classes: 

(1) Pores, which are present in pieces fired at low 
temperatures, due to the incomplete consolidation of the 
clay. These are the original interstitial spaces of the un- 
burnt clay. 

(2) Blebs or bubbles, which are formed in the glass 
at higher temperatures by the liberation and expansion of 
gases. 

Pores of the first sort are of small size and irregular 
outline. As the temperature increases, and the material of 
the matrix gradually fuses into glass, these interstitial 
spaces tend to disappear. 

Cavities of the second sort, which we may for conven- 
ience designate as blebs, are simply gas bubbles in glass. 
They are circular in outline and vary greatly in size. They 
are not present in the bricks burned at lower temperatures, 
but appear only after the formation of considerable glass. 

DESCRIPTION OF SLIDES. 

The K 3 Series. R 3—14. This brickette was drawn 
at cone 3, or about 1190° C. The color is red. Under the 



PYKO-CHEMICAL AND PHYSICAL, BEHAVIOR OF CLAYS. 31 

microscope, the earthy matrix or ground mass is dark 
broAvn, the color beiug due to the presence of irou oxides. 

The mineral frai>nients are quartz, feldspar an<l mica, 
named in the order of their abundance. They are angular . 
in outline; the thin edges being sharply defined. 

Glass has formed to some extent throughout the 
ground mass, and in a few instances it has separated out 
into clear transparent masses, in seA'eral of which blebs ap- 
pear. The blebs, however, are so few and so small that the 
cavities may be considered as made up aiiuo.st entirely 
of pores of the first class. As estimated under the micro- 
scope, the porosity is 1.9%. 

R 3 — 16. Drawn at cone 5, or approximately 1230° C ; 
color dark brown. Under the microscope the ground mass 
appears somewhat denser and darker than in R 3 — 14. The 
quartz fragments are apparently unchanged. The feldspar 
fragments, however, have disappeared.^ Mica is present, 
but in very small quantity. 

Glass has been formed in considerable amount. It ap- 
pears in clear transparent areas, aften 0.1 M.M. in diame- 
ter. In some of the glass, needle-like crystals have begun 
to form, but where free from these the glass is colorless. 
This fact would seem to indicate that but little iron has 
entered into its composition. 

As stated above, fine needle-like crystals are often 
present, imbedded in the glass. They do not appear to have 
any definite arrangement with respect to each other, but 
occur singly or in dense masses. When viewed singly they 
are colorless, but when seen in masses, they possess a 
greenish yellow tint, which they impart to the glass in 
which they are imbedded. What the crystals are was not 
determined. 



(1) Hiutze prives the fusion points of the feldspar as ranging from 
1140°O. in sanidine to 1230 C in labradorite. In the brickette under 
consideration it is evident that the feldspar has fused into p:laas. It 
is to be supposed that in this fusing, it would flux some of the quartz. 
If it did so, howevpr, tlie quartz must have been furnished by the 
j?round mass, for the coarser fragments are apparently not changed 
in outline nor diminished in amount. 



32 PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 

The iron oxides present in the matrix have become se- 
gregated into dense masses, which, where they transmit 
light at all, show the red of hematite, but no definite crys- 
tals are to be seen. Pores of the first class have disappeared, 
and blebs in the glass have become numerous and large, 
their average diameter being 0.066 m.m. The estimated 
pore space has increased to 4.2%. 

K 3 — 18. Drawn at cone 7, or 1270° C. The fragments 
of quartz appear unchanged. The earthy ground mass is 
rapidly fusing into glass, which has increased greatly in 
amount over that in the preceding slide. The fine needle- 
like crystals are also present in greater number. 

Minute crystals of iron oxide are seen, apparently in 
the form of rhombohedrons, having slightly concave faces. 
They do not exceed 0.0014 m.m. in diameter. The blebs 
have an average diameter of 0.1 m.m. and the pore space 
has increased to 12.0%. 

K 3 — 20. Drawn at cone 9, or approximately 1310° C. 
Quartz fragments are present as before, but occasionally 
one is observed the edge of which have fused into a j^lass. 
The needle-like crystals are everywhere present in the 
glass, giving to it the yellowish-green tint before men- 
tioned. The iron oxides appear much the same as in the 
last specimen. The blebs are but little changed. 

E 3 — 22. Drawn at cone 11, or approximately 
1350° C. The earthy matrix has given place entirely to 
glass. 

Quartz fragments are still present, but thin; their 
edges have been rounded by fusion. 

The fine needle-like crystals in the glass have increased 
greatly in length, being in some cases 0.03 m.m. long. They 
exhibit for the first time a marked tendency to collect in 
radiating clusters. Often they appear to be attached to the 
corners of the crystals of iron oxide. These latter have 
increased in number and size, being 0.005 m.m. in diameter. 
In some cases the individuals unite, forming long serrated 
columns. 



PYRO-CHEMIOAL AND PHYSICAL BEHAVIOR OF CLAYS. 33 

Blebs have increased greatly in size, their average di- 
ameter being 0.128 m.m. The pore space as estimated from 
them is 19%. 

The G II iSeries. G 11—10. Drawn at cone 02, or 
approximately 1110° C. Color, brick red. 

As in the series already described, the mineral frag- 
ments consist of quartz, feldspar and mica. Very little 
glass seems to have developed at this temperature, and no 
blebs are present. The pore space is made up entirely of 
pores of the first class, or those due to the imperfect con- 
solidation of the bricks. The average diameter of these 
pores is 0.065 m.m., and the pore space as calculated is 
2.6%. 

G II — 12. Drawn at cone 1, or approximately 
1150°C. Color red. 

A little glass appears, but no blebs are seen. The av- 
erage size of pores is lower than in the last slide, being 
0.045, but the pore space as estimated runs a little higher, 
or 3.6%. 

It may be remarked that in the slides studied there is 
no marked increase in the pore space, as temperature in- 
creases, up to the point where blebs appear. From that 
point on, pore space increases rapidly. 

G II — 14. Drawn at cone 3, or approximately 
1190° C. Color, reddish brown. 

Fine needle-like crystals have formed in the glass. A 
few blebs appear, but are not in sufficient number to affect 
the pore space materially. As estimated it is 3.2% while 
the average size of the pores of both classes is 0.06 m.m. 

G II — 15. Drawn at cone 5, or approximately 
1230°C. Color, dark brown. 

Quartz fragments are still present, but the feldspar and 
mica have disappeared. Glass has formed in great quan- 
tity, being colorless, or when acicular crystals are present, 
greenish yellow. These crystals are present in great num- 
bers and resemble those described in the former series. 
Microlites of iron oxide are also present, but have not yet 
grouped themselves in dendritic forms. Pores other than 



34 PYRO-CHEMICAL, AND PHYSICAL BEHAVIOR OF OLAYS. 

blebs have disappeared, but the blebs have increased greatly 
in size, the average diameter being 0.175 m.m. while the 
pore space amounts to 12%. 

Generalized Summary of Changes observed at different 
Heat Treatments. 

Cone 02. — Quartz and feldspar fragments are unchanged. 

But little glass is developed. 

Iso blebs have yet formed. 
Cone 1. — No marked change has taken place over cone 02. 
Cone 3. — A small amount of glass is developed from the 
ground mass. 

A few blebs appear. 

Needle-like crystals are developed in the glass. 
Cone 5. — Feldspar fragments are fused into glass. 

Quartz fragments are unchanged. 

Blebs increase in number and size. 

Minute crystals of iron oxide develop. 
Cone 7. — Glass increases in amount. 

Blebs increase in number and size. 

Quartz fragments are unchanged. 
Cone 9. — Quartz fragments begin to fuse into glass along 

their edges. 
Cone 11. — Ground mass is completely fused into glass. 

Some rounded quartz fragments still remain. 

Blebs have increased remarkably in size and 
number. 

Microlites are more numerous. 
It should be borne in mind that this is but a prelimi- 
nary study. The number of slides examined is too limited 
to warrant broad generalizations. 

Carroll H. Wegemann. 

Assistant in Geology, University of Illinois, 

Owing to the absence of similar data on other clay 
samples and the incompleteness of the present researches, 
the writers have no definite conclusions to present con- 



I 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 35 

oerning the surprising facts presented by Mr. Wegemann. 
This data does, however, establish the facts that neither a 
mineralogical analysis nor an ultimate or rational analysis 
of clay will give indication of the nature of its pyro-chemi- 
cal and physical behavior. Indeed, the above data would 
seem to throw doubt on the value of a pyro-chemical and 
physical study of a synthetical mixture of minerals as a 
basis on which to interpret the thermal changes in an 
"unknown" clay mixture. 

In the following curves, plates IV and V, are shown 
the specific gravity, volume shrinkage and changes in 
porosity in the two clays of which microscopic studies were 
made by ^Ir. Wegemann. It will be seen that all three fac- 
tors decrease simultaneously, showing that the increase in 
bleb structure is not sufficient to counteract the shrinkage 
of the mass as a whole, and is not to be accounted for by 
the sealing up of the original pores. 

If the minerals and the iron do not enter into the 
thermo-chemical reactions, as has been heretofore supposed, 
and if the thermo-physical changes are dependent entirely 
upon the chemical changes, it is at once obvious that the 
potency of tbe influence of size of grain, adsorbed and pre- 
cipitated substances, has been demonstrated. 

CLASSIFICATION OF CLAYS. 

On the basis of the characteristic differences in tlieir 
pyro-chemical behavior, a few of the clays tested in this 
investigation have been grouped into types as follows : 

1. No. 1 Fire clays. 

2. No. 2 Fire clays. 

3. No. 3 Fire clays. 

4. Paving brick shales. 

5. Building brick shales. 

Further differentiation of these clays is possible; for 
instance, clays exhibiting change in porosity with suc- 
cessively increasing heat treatment similar to that of V. 2, 
shown in the following curves, may be classed as sewer 
and side walk brick clays. (See porosity and sp. gr. curves 
forV. 2). 
& Nf.-a. 



38 



PYRO-CHEMIOAL AND PHYSICAL BEHAVIOR OF CLAYS. 




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PYBO-CHEMIOAL AND PHYSICAL BEHAVIOR OF CLAYS. 



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PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 





TRANS 


AM. CER. 


soc 


VOL 


IX 






PURDY AND MOORE. 


PLATE VI 












































































































































































































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NO a fire: clay 




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TEMPERATURES CXPRESSeO IN COWCS 



Curve showing changes in porosity of clay V 2, at different 
temperatures. 



PYRO-CHEMIOAL AND PHYSICAL BEHAVIOR OK CLAYS. 39 





TRANS. 


AM CER.'50C''voClX 






PL/RDY'aNO MOORE PLATE VII 


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NO. 2 F1R£ CLAV 


























































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TEMPERATURES, EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay V 2, at different 

temperatures. 



40 PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 

While such clays vitrify too rapidly to produce tough 
bricks, such as are demanded for street paving, they become 
impervious to water at low temperatures and do not soften 
by fusion with increase of heat ranging over several cones, 
or swell because of the generation of gases from the interior 
of the brick. In other words, while bricks made from such 
clays are brittle, they are rendered hard and impervious to 
water at comparatively low temperatures, and at the same 
time have a relatively wide heat range before failing by 
complete fusion, or becoming distorted by expansion of 
gases in their interior. 

The writers have not had suflflcient experience with 
this method of classification to justify them in offering a 
complete scheme for the grouping of clays, aud have there- 
fore suggested only five classes. 



NUMBER ONE FIRE CLAYS. 

The writers of Clay Reports have heretofore failed to 
recognize that of two clays having similar ultimate chemi- 
cal compositions and similar ultimate fusion periods, one 
can be used in No. 1 fire brick, while the other would fail 
utterly as a fire brick material, and that the one failing as 
a fire brick material would be the only one that could with 
success be used in the stone ware industry. Several exam- 
ples of the foregoing were noted in the examination of the 
Illinois fire clays. In fact, the case is not an uncommon 
one. 

In fire brick, maintenance of an open structure 
through the entire heat range used in the various ceramic 
industries is essential. On the other hand, in stoneware, 
closeness of structure at comparatively low temperatures, 
or early vitrification followed by a long fusion range is 
absolutely required. It is evident, therefore, that a classi- 
fication of refractory fire clays (so called because they 
withstand heat equivalent to cone 27 or more without fail- 
ure) should take account of this difference in their manner 



PYBO-CHEMICAl, AND PHYSICAL BEHAVIOR OF CLAYS. 



41 



of fusion. This essential difference in the behavior of fire 
clays is recognized in the tentative scheme of classification 
here presented. 

It will be noted that these clays show comparatively 
little decrease in porosity from cone 010 to cone 11. This 
decrease averages from 7 to 15% of the initial porosity 
and in no case does it exceed 17%. 

The specific gravity remains fairly constant from cone 
010 to cone 3, and then, even in the purest clays, it begins 
to decrease slightly. This decrease in specific gravity in 
the No. 1 fire clays, even when the porosity remains very 
high, is considered as evidence of the influence of the ad- 
sorbed or cementing salts which, while constituting but a 
very small part In- weight of the whole, are nevertheless the 
potent factor in causing fusion. 

The chemical comx)osition and ultimate fusion point 
of these clays as determined in the chemical laboratory of 
the University of Illinois, under the supervision of Profes- 
sor S. W. Parr, are as follows: 



Sample 
Number 


Moisture 


Volatile 
Matter 


SiO, 


AljOj 


Fe,0, 


TiO, 


Total 


Fusion point 


H. 24 


0.6 


4.63 


76.10 


15.31 


1. 10 


1.31 


99.06 


30 


V. 11 


1.74 


10.28 


66.28 


26.68 


8.24 


1.29 


99.60 


Not reached 


F. 18 


0.84 


6.66 


66.88 


21.87 


2.23 


1.18 


99.86 


29 


F. 19 


1.19 


6.31 


68.12 


20.08 


1.76 


1 16 


98.62 


31 



42 



PYBO-CHEMIOAL AND PHYSICAL BEHAVIOR OF CLAYS. 





TRANS. 


AM CER 


SOC VOL, IX 










PUROV ArvJO MOORE, 


PLATE IX, 


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I FIRE CLAY 


































































































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TEMPERATURES, EXPRE&SE.O JtS CONES 

Curve showing changes in porosity of clay F 5, at different 
temperatures. 



i 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 43 





TRANS 


AM CER SOC VOL IX 






PUROV AND 


MOORE. 


^LAT^ X 






' ^ 


. 








\^ 








( 







25 














^V 




k 




















\ 


1 ^ 


iJ 










































> 
t 






















^1„ 






















M 
U 
Ol 

13 










































































































t* 























OO C^ 06 O* 02 I 3 S 

TEMPeRATURE^, EXPRESSED IN CON E5 



Curve showing changes In specific gravity of clay F 5 at different 

temperatures. 



44 



PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 





TRANS 


AlVI CER SOC 


VOL 


IX 




PURDY 


AND MOORE. PLATE XI 




























































































































































































1 1 




in 












1 

j 


u <^ 


1 


— < 


"-^, 






1 


Q. 
Z 
O 






^V 




. ^ ^ 


! 














\ 




1 
1 


iji 














\ 


1 




I 














\ 


i 




> 














> 




L^__^^ 




H 
S 


















^ 


kw 


2 




















T 
























10 


















































F 18 

NO 1 FlRE CLAV 
CONE OF FUSION 30 - 












































































o 























TEMPERATURES. EXPRESSELD IN CONES 



Curve showing changes in porosity of clay F 18, at different 
temperatures. 



PYKO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 



45 



Z7 


TRANS 


AM CER SOC 


VOL. IX 






PURDV 


AND MOORE. PLATE XII 


1 












K 


L 










^ 


zs 
i3 

2 3 
> 

r 

o 

ll 

U 

U 

a 




























N 


























































































































le 




































































1 b 




FI8 
NO 1 FIRE CLAV 

CONt OF Fu6lOt4 30. 


































i« 














1 











lO 


e 


b 


* 





2 








■ 


5 


II 



TEMPERATURES, EXPRESSED IN CONES 

Curve showing changes in specific gravity of clay F 18, at different 

temperatures. 



46 



PYRO-OHEMICAIi AND PHYSICAL BEHAVIOR OF CLAYS. 





TRANS 


AM CER 


soc. 


VOL IX 






PUROY 


AND MC 


>ORE. 


Pi 


^TE Xdl 


OO 
















































































































































































t- ■■ 
Z 
uJ 
-J 30 






























































' 


0^ 1 






*^ 


z . 




N 




^ 1 










D 








1 ) 


\ 






. 


Ui 

a. 












\ 




















\ 








O 
















t**"^ 


,_^ 




1 

1 












] 


U 
O 
0. 




















i 




















i 






















































F19 

NO 1 FIRE CLAV 








































1 




































f 





















.TErvtPER/VTURES EXPRESSED IN CONES 



Curve showing changes in porosity of clay F 19, at different 
temperatures. 



PYRO-CHEMICAL AND PHYSICAL, BKHAVIOB OF CLAYS. 47 



'■> 


rPANS 


AVI CER 50C VOL. 9 








PURDV 


AND! MOOBE, 


PL^TE. XIV 






_, ._ ., 


~^ — i — 


^-^ 


^^ 






c 


"^ 














I 

! 




X 




"""^1 


i* 






















< i 










































1 


> 

r 

s 












































Ojo 




















1 




















1 


o 

bJ 

a 
If),, 








1 

1 












1 


18 


































— 


F 


19 


. 





















CONC OF FUSION JO* 


























14 























oio oa o6 04 oe I 3 5 

TEMPERATURES, EXPRESSED IN CONE.' 



Curve showing changes in specific gravity of clay F 19, at different 

temperatures. 



48 



PYBO-GHBMICAL AND PHYaiOAL BEHAVIOR OF CLAYS. 





TRANS 


AM. CER SOC 


VOL 


IX 




PURDV 


AND M 


OORE. PLATE XV 


































































































































































































































rs. 








W_ 










a. 




'J 
a. 




N 


r^ 






^ 










a 
















"•*^ 


L 




u 












. 






\ 




(L 
X 


















N 


i 


o 










































g 




















1 






















t 






















-4 
































H 24 

NO.I FIRE C1_AV 




































































































TEMPERATURES EXPRESSED IN COISES 

Curve showing changes in porosity of clay H 24, at different 
temperatures. 



PYBO-CHEMICAIi AND PHYSICAL BEHAVIOR OF CLAYS. 49 





TRANS 


AlVl CER SOC VOL IX 








PUROY 


AND MOORE,! PLATC XVI 
























•"t 








_ 






-^ 


kw 






















N 


k. 


^J 




















N 






















>- 

1- 

1" 

O 

o 
o 

UJ 
Q. 








































































































































H 24- 

Not FIRE CL.AV 




































r 4 

























"O Ot 


3 o 


•J o 


4- 





2 












II 



TEMPCRATURES EXPRCSStO IN CONES 

Curve showing changes in specific gravity of clay H 24, at various 

temperatures. 



50 



PY BO-CHEMICAL AND PHYSICAL, BEHAVIOR OF CLAYS. 



TRANS. AM CCR. SOC VC ' IX 



PURDY AND MOOPE. PLATE XVU 









i __L.___ . 














1 ! 


















1 
























1 




































































































































































( 


^.-— ^ 


L 


k^ 






















^**<^ 


L^ 


^ 


























Kv 






















^ 


k 






















^*v 


r*^ 


kv 






















> 
































































































V n 

NO 1 FIRE Cl_A,V 


































































































TEMPERATURES. EWRESSED IN CONES 



Curve showing changes in porosity of clay V 11, at various 
temperatures. 



PYRO-CHEMICAL AKD PHYSICAL BEHAVIOR OF CLAYS. 51 



TRANS. AM CER SOC VOL. IX 



PURDV AND MOORE PLATE Xvui 



o 
o 

o 



1„ 1 


1 
























' ' 


' ^ 






k 














N 






^^ 












































































































































. 














































vu 

NO 1 FIRE CLAY 



















































010 06 



O* 02 I 3 5 

TEMPERATURLS. EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay V 11, at various 

temperatures. 



P. & M —4. 



PYRO-OHBMIOAIi AND PHYSICAL BEHAVIOR OF CLATS. 



5S 



NUMBER TWO FIEE CLAYS. 

A few number two fire clays are represented 
in the following collection of plates. It will be noted that 
while the decrease in specific gravity of this group of clays 
is about the same as that shown in the No. 1 fire clays, the 
porosity shows a much larger decrease. The early vitrifi- 
cation and slow fusion is quite pronounced in this group, 
permitting their use in the paving brick, sewer pipe, stone- 
ware and terra cotta industries, but not in the manufacture 
of No. 1 fire brick. 

The chemical analyses of two of these clays, made in 
the chemical laboratory of the University of Illinois, under 
the supervision of Professor S. W. Parr, are as follows : 



Sample 1 

Number | Moisture 


Volatile 1 
Matter | SiO, 


Ai.o. 


Fe.O, 


TiO, 


Total 1 Fusion point 


V. 4 
K. 12 


2.37 
0.60 


8.84 

10.09 


64.80 
54.37 


29.44 
23.61 


1.70 

6.14 


0.82 
fluxes 

6.97 


97.97 
100.78 


■ot reached 
not deter'ed 



54 



PYRO-OHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 



TRANS. 


AM. CER. SOC 


VOL tX 




PURDY ANO MOORE. PLATE XIX 
























































































































































































































































^ 






















^^ 






L 














^^^^ 












\ 


^ 




















\, 




















S 
























k 




















^ 


k^.^^^ 
















































NO. a FIRE CLAY 

























































































TEMPERATURES. EXPRESSED IN CONES 



Curve showing changes in porosity of clay F 4, at different 
temperatures. 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 65 





TRANS 


AM CER 


SOC VOL IX 










PuRtTY AND 


MOORE 


PLATE XX 


ZJIk 

zs 




















/ 












^ 


\ 




















\ 








> 

< 

O 




















^ ^. 






























































O 
IJ 

a 
































































































F 4. 

NO 2 FIRE CLAV 


































• 

























vw wo VO V*- U£ ' -J -J ' J ' < I 

TEMPERATURES, EXPRESSED IN CONES 

Curve showing changes in specific gravity of clay F 4, at different 

temperatures. 



66 



PYBO-OHEMICAL AND PHYSICAIj BEHAVIOB OF CLAYB. 





.TRANS 


. AM. ceR. soc. 


VOL 


O. 






PVJROY 


/>*40 MC 


)ORE, Pi 


.ATE. XXI 










. 
















■ 






















/ 










































40 


* 


























' 








































i 


















<n 






















'z 






















a < 




r*"*^. 




















Z 




s 


s^ 


















ij 






N 






















""""^ 


S-^^ 












> 
t 












\ 




















> 


k 




















\ 




















\ 






























10 




















J) 














. 
















F2I 

NO. e riRE CLAV 
CONE OF Fusion £9 












































































o 






















c 


lO O 


B O 


b O 


^ 


o 


z 




i 


i 




? 


3 II 



TEMPERATURES. EKPRESiED IN COtSES 



Curve showing changes in porosity of clay F 21, at different 
temperatures. 



PYRO-OHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS, 



57 





TRANS. AM. 


CER SOC 


. VOL IX 




PUROV ANDlWOORE. 


Plate xxk 


2Ji 

2J 


^ 










H 


S^ 




















"V, 






1 


22 






~ 






! 
1 


! 






— 




>- 
1- 












i 
1 




































o 




















































o 


























16 














~ — - 









t (^ 












F 


2» 
















































< 


,OME or .f 


VSION 2J 


LJ 












14- 























oto oo 



0<> 04- OZ. I 3 5 

TEMPERATURES. EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay F 21, at different 

temperatures. 



58 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOK OF CliAYS. 



TRANS AM CER SOC VOL. IX 



PWRDY AND MOORE. PLATE! XXlll 





















































































































* 






























































































































rx 






















\ 




















\ 




















\ 


^ 




\ 














T 


1^ 




V 




















N 


w 




















^ 
























i^ 


*"**4 




























V4- 

NO a FIRE CLAV 

























































































TEMPERATURES. EXPRESSED IN CONES 

Curve showing changes in porosity of clay V 4, at difEerent 
temperatures. 



PYRO-CHEMICAl. AND PHYSICAL BEHAVIOR OF CLAYS. 59 



( 

2i 


TRANS 


AM CE 


R SOC 


VOL 


K 


1 — 




PURDV f 


kNO 


M0< 


OPC. 


PL^ 


sTE XXW 


2 J 

> 
> 














































o 


























o 
u 
Q. 

19 




















1 














V 


A- 


— 












































CO 


HE or FUSION 


NOT AT TA INC 


° 














V* 























TEMPERATURES. EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay V 4, at different 

temperatures. 



PYBO-CHEMICAL AND PHYSICAIi BEHAVIOB OF CLAYS. 61 



NUMBER THREB FIRE CLAYS. 

In the following ten pages are shown the porosity and 
specific gravity curves of a class of clays which in the 
judgment of the writers, ought to be put in a different 
catagory from the preceding group or number two fire 
clays. Heretofore, both have been classified together in- 
discriminately in ceramic and geological literature, as 
number two fire clays, but they are not the same. Clays 
of this class differ from the No. 1 and No. 2 fire clays, in 
that they seldom have a fusion point exceeding cone 16 or 
17, fuse in a very irregular manner, and exhibit a much 
larger decrease in specific gravity owing to the presence 
of iron in nodular form as sulphides or carbonates. 



62 



PYRO-CHEMIOAI. AND PHYSICAI- BEHAVIOR OF CLAYS. 





TPANS 


AM CER SOC VOL IX 








PuROV AND .MOORE PLATE, xxv 




































































































■4-0 






































































(0 
























1- 
z 
u 














1 








u 
a 
a 

r 
























[V 




















\ 


















UJ 

If) 




> 


\ 








i 








u 

X 

a 

)<; 

u 

.20 
>- 






\ 






















\ 




. i 














\ 






j 

















\ 






1 










o 

Q. 






\ 


^ ^ 


' 


r\ 
























\ 


























\ 




















1 






\ 














F7 

N4 3 FIRE CV.AV 

CONE CP FUSION 1* 


\ 














\ 




















\ 


k. 








































^^^ 














p 


C 

























TEMPER/KTTJRES, EXPRESSED IN CONES 



Curve showing changes in porosity of clay F 7, at different 
temperatures. 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 63 





TRANS. 


AM. 


CER 50C 


VOL ix: 








PUROY AND MOORE. 


Plate xxvi 


< 
































>«». 


























N 




-^ 




k 








2* 












1 


\ 
























N 


^^^^■■■^o 


/I 





























> 
























































u 




























o 
u 
a 
o 












































































r- 


F7 


— 










' 4> 














Nv^ J rir\L ».l_/-\T 



























( 


.ONL OF F 


L/SlOM lA 


^ 













OlO Oa C«> O* 02- I 3 i 7 9 

TEMPCRATURE.S EXPRESStD IM CONES 

Curve showing changes in specific gravity of clay F 7, at different 
temperatures. 



«4 



PYBO-OHBMIOAIi AND PHYSIOAI. BEHAVIOR OP CLAYS. 





TRANS AM CER SOC VOL. 


IX 


, PUROY AND MOORE PLATE XXVll 


















































































































































































h 

z 






















r — 


kv 


















(£ JO 
Q. 






k. 
















Z 




1 


\ 
















Q 
bJ 

a. 

a. 






N 


Nil 




















V, 


^^ 


k. 






















\ 










>- 

h 












\ 










o 

or 












\ 


A 








o 

0. 














\ 






















\ 








lO 














\ 


^ 






















\ 












(T sn 














NO. 3 FIRE CLAY 

CONE OF FUSION £9 




\ 


















> 


N 












































^ -J 


« 






















c 


10 o 


8 


6 


4- 


c 


>2 




i 




5 


7 


9 1 



TEMPERATURES. EXPRESSED HN CONES 



Curve showing changes in porosity of clay F 20, at different 
temperatures. 



PYRO-CHEMICAL AMD PHYSICAL BEHAVIOR OF CliAYS. 65 





TRANS 


AM CER. SOC 


VOL. 


IX 








PURDY AND 


MOO«£.. 


PLATE X, 




^- 










\ 










<^ 


^****-^ 








2S 












\ 




















\ 






























k^ 




























> 






















o 






















o 
u 
a 

IT) ,T 
































































































F20 

MO 3 FIRE CLAY 

CONE OF FUSION Z» 



























































Cunre showing changes In specific gravity of clay F 20, at different 

temperatures. 



66 



PYRO-CHEMICAL AND PHYSICAL. BEHAVIOR OF CLAYS. 



TRANS AM. CERSOC VOl_ IX 



PURDV AND MOORE PLATE XXIX 




TEMPERATURES, EXPRESSED IN CONES 



Curve showing changes in porosity of clay K 12, at different 
temperatures. 



PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 67 





TRANS 


AM CER SOC VOL IX 






PURDY 


AND MOORC. PLA'rt XXX 




^ 


f ^ 








\ 










It 
















N 


V 






















\ 


\ 






i 

r 


















\ 


1 
\ 


















N 












































u. 
o 

5,. 






















































































Ik 




K12 

vJO 3 FIRE CLAY 










f 






















1 * 

























.0 o 


a o 


«> o 


* o 


z 




s 




5 




9 > 



TEMPER ATURE.S. EXPRESSED IN CONES 

Curve showing changes in specific gravity of clay K 12, at different 

temperatures. 



p. & M.— 6. 



68 



PYBO-CHBMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 





TRANS AM CEP SOC VOU 


IX 




PUROY 


AND MO0f?E,. PLATE XX 






































































































































































1 










h 

7 






















u 






































■z J 


J 


^^ 


















Q 

in 




s 


kv. 




1 
1 










CO 

u 






1 


k^ 














w 

20 
>■ 








^ 




V 




















\ 










<n 
o 
a: 
o 










> 


^ 




















\ 




1 
















\ 








to 








1 
1 




\ 


^ 














1 








V 










R 1 

NO 3 RRE CLAY , 
















^ 






























































o 




1 















TE.MPERATURE.5. O'-PRESSEO IN CONES 

Curve showing changes in porosity of clay R 1, at different 
temperatures. 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYB. l69 



27 


TRANS 


AM CI 


IR. SOC 


VOL 


IX 




1 1 


PUROY 


AND MO 


ORE. 


PLATE XKXl 
1 t 


:,. 










— . 


K 











2- 














\ 


^ 


»__ 




12 

> 

I'' 
















1 

1 
1 





























^7r 












1 


I 








o 

Q. 




















.A 





































R 

I0.3 FIF 


1 

JE CLA^ 


' 





























1 4- 


f 


! 



















OlO OS Ofe 04- 02 I J 5 

TEMPERATURES. EXPRESSED 'N CONES 



Curve showing changes in specific gravity of clay R 1, at different 

temperatures. 



70 



PYRO-OHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 





TRAMS 


AM CEP SOC 


VOL 


X 




PURDY AND MOORE. PLATE XXXItl 






1 
1 














1 




































! j 














- . AO 


i 














1 

1 














h 
Z 

UJ 

<J 
Or 

z 
a 


1 1 
















1 








i 
1 


1 1 
1 


























1 1 

1 ! 






A. 


1 
1 








1 






\ 
















u 
a 






\ 




















\ 






L 










0. . 

y 

hi 


















\ 










> 

in 
O 












\ 






















k 






1 


o 
a 














\ 






















> 


k 




10 
















\ 
























> 


P"^**^ 








V5 

tvJO 3 FlRE CUAV 
CONE OF FUSION 31 




















N 


















\ 




































T) 


























06 O* OZ I 3 _ 

TEMPERATURES EXPRESSED IM COMES 

Curve showing changes in porosity in clay V 5, at different 
temperatures. 



PYBO-CHBMICAL^ANO I'HYSICAIj BEHAVIOR OF CLAYS. 71 



i7 


TRANS 


AM 


CE 


R SOC 


VOL. 


\X 






PUROV 


AND M 


OORE, 


PL 


-ATE XXX 


V 


( 
2* 

> 


kl 




^^ 






\ 




, 


^^ 




i 




— 








- 










^N 


-^ 




> 


h 

o 


























































o 






























o 
u 
























18 


. 

































1 

V 


5 
























CONE or rtlSlON 31 



















































08 Ob 



TEMPERATURtS, EXPRESSELO IN CONES 



Curve showing changes in specific gravity of clay V 5, at different 

temperatures. 



72 PYRO-CHEMICAL AND PHYSICAL BEHAVIOB OF CLAYS. 



SUMMARY OF FIRECLAY GROUP. 

The manner and amount of decrease in porosity and 
specific gravity between these three groups is quite marked. 
Similar curves drawn from data obtained on clays other 
than those here reported, exhibited similar differences. In 
the laboratory the clays were known only by sample num- 
ber, the field data being ignored to prevent possible preju- 
dice, but in no case did the inferred "possible uses" of the 
clay disagree with data obtained in the field concerning 
their commercial use at the present time. So far then, as 
the evidence thus obtained is concerned, it can be stated 
that this method of classifying fire clays has succeeded 
where other methods have failed. 



PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 73- 

PAVING BRICK SHALES. 

The standardization of tests for first class paving 
brick clays has been and perhaps will be for some time 
ing brick clays has been and perhaps will be for some time 
the subject of much consideration by ceramic investigators. 
The tests here reported can be said to give negative rather 
than positive information, in that they very effectively 
differentiate the clays that cannot from those which may 
be utilized in paving brick manufacture. Judging from the 
results so far obtained, they fail, however, to differentiate 
the paving brick clays one from another in regard to their 
comparative quality. For example, we have not been able 
to distinguish by these tests between the clays of 14% type 
and the 24% type, measured in percents of loss in the ratt- 
ler test, nor between the clays that preserve their maxi- 
mum strength through a wide heat range and those which 
attain and preserve their maximum strength only within a 
very narrow heat range. 

The cause of failure of the pyro-chemical studies in 
this respect is, no doubt, to be found in the fact that inher- 
ent strength is not wholly a function of rate of vitrification 
or development of vesicular structure. Tensile strength 
of the raw clay, fineness of grain, and many other physical 
and chemical tests have been made on paving brick clays 
in order to determine the relation between their properties 
and the strength of the burned ware, but after a study of 
25 paving brick clays from different states, it has been 
found that but very little relation exists. The pyro-chemi- 
cal studies here reported are the only ones that give any 
clue to the toughness or strength of the burned ware. 

Pyro-chemical studies similar to those here outlined,, 
together with a determination of the maximum strength 
and the range temperature in which this maximum 
strength is developed, would enable the observer to pro- 
perly classify and differentiate paving brick clays. This, 
however, amounts to a sub-classification of the paving 
clays on a basis different from that of the main sub-divi- 
sion. 

The following are typical porosity and specific gravity 
curves for clays of the paving brick type : 



74 PYRO-CHBMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 





TRANS AM 


CER SOC VOL. IX 




PUROY 


AND MOORE,. PLATE XXX 


























































































f i 














1 
















ill! 
















1 i 






<0 1 


^ 








i i 






z 

-UJ 

« 

Ui 

a 

z 


^*Vj 


^-^. 






i 


1 








^ 


\ 




: , i 










\ 


1 ■! 






o 

Li 






\ 


! 1 ! 




a. 






N 


^ 


1 

1 










a 








\j 




! 

! i 




y 
t 

10 

o 
o: 
o 

Q. 










Nj 


t 1 

- 1 i 












^ 
















>vl 














i\ i 




«0 










\ 












1 


\ 


1 






K6 

-WING BRICK SHALE 
BATTLER LOSS L3 2S 


\ 








" 






p 


\ 


















\ 
































\ 


L ._ 


S 


























TEMPERATURES. EXPRESSED IN CONES 

Curve showing changes in porosity of clay K 6, at different 
temperatures. 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 75 





TRANS 


AM CER 50C. VOL IX 






PUPDY 


AND 


MOORE. 


PLATE XXHV 


























■ i 


■ 


^^ 




























X 


\ 






















\ 






























> 

!■■ 






































K 




o 
bi 
a. 


















\ 






















\ 


, 






















































K6 

PAVIMG BRICK SHALE 
Rattuer loss 13 25 




































1 ♦ 























OtO on 



Te.MPEr?ATURES EXPRE^StD IM CONES 



Curve showing changes in specific gravity of clay K 6, at different 

temperatures. 



76 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 



'80 



^TRANS." AM CeR SOC • VOU' IX 



. puRDv AND t^ooRC, Plate xxxvii 















































































































































""^^^ 


■ — ^ 




















































"*'*^ 






















1 




















\ 




















\ 




















\ 




















\ 




















\ 




















\ 




















\ 




















1 


\ 




















\ 
























\ 










R3 

Paving brick shale 
»»ATT(.E« Los» i*.eo 


\ 


' 








\ 


















r\ 


































"V*^ 

























5 06 O* 04 02 I 3 67 9 

TEMPERATURES, EXPRESSED IN CONES 

Curve showing changes in porosity of clay R 3, at different 
temperatures. 



PYBO-CHEMICAL, AND PHYSICAL BEHAVIOR OF CLAYS. 77 



TRAN5 AM CER SOC, VOL IX 



PURDY AND MOORE. PLATE XXXVMI 







- 


_ 


















t i 




















[N. 




















N 


V 






















\ 
























\ 






















\ 




Of 




















y 



u 
Q. 






























• 
































































R3 

PAVIN6 BRiCK SHALE 

RATTLER LOSS U* tO. 




















1 














. 

























om 06 CO 04 



TEMPERATURES. EXPRESSED IN CONE: 



Curve showing changes in specific gravity of clay R 3, at different 

temperatures. 



78 



PYRO-CHEMIOAL. AND PHYSICAL BEHAVIOR OF CLAYS. 



TRA-rJS 


^M CER SOC 


VOL 


IX 


PURDY AND MOORE PLATE XXX rX 


































































1 
i 














! ! 


























































\ 




















N 


















>> 


K^ 




















^*«*^ 


r"*^ 


^ 




















\ 




















\ 




















> 






















\ 




















\ 




















\ 




















\ 




















\ 




















1 


\ 










K 1 

PAV1M6 BRICK SHALE 










1 


P^^ 


















^> 


i\ 






i 






















\ 


^ 























TE-MPERATURES, eXPR£.SSEO IN CONEJS 

Curve showing changes in porosity of clay K 1, at different 
temperatures. 



PYBO-CHEMICAL, AND PHYSICAL BEHAVIOR OF CLAYS. 79 





TRANS 


AM 


C 


ER SOC 


VOL 


IX 






PURDV 


AND moors: plate XL 


< 

2£ 






-^ 






^ 


L 


[ 








Zi 
Z* 












— 


X 









2J 

a. 














—A 


k 





























^-n 
























O 

U 
Q. 

te 
















1 " 

















— 


K 


1 


"~ 




_ 




f 






































lATTLER L< 


3SS 15 8: 


J 










L* 























oio oe 06 o* oz 

telmperatureg expressed in cones 

Curve showing changes in specific gravity of clay K 1, at different 

temperatures. 



80 



PYRO-OHEMICAIi AND PHYSIOAL BEHAVIOR OF CLAYS. 



30 


TRANS 


AM CEP SOC 


VOL 


IX 






PUROV 


AMD- MOORE. 


Pl_ATE XV.I 


































■ 






















































*0 












































\ 






















\ 




















J1 

h 
Z 
u 






















1 


\ 


















IL 




N 


















r ■ 






\ 
















o 
u 

(t . 

Q. 
X 






\ 




















N 


\^ 




















\. 


L 












)- 










"V 


r\ 










O 












\ 


l\ 






















\ 






















\ 








(O 














\ 
























\ 












J 2 

PAVING BRICK SHALC 

RATTLER LOSS \-r lA 


V 






• 






V 


















\ 


N^ 




































^^^ 


^^^^^ 























^^ 


) 



TCMP£RATURES. EXPRESSED IN COINE3 



Curve showing changes in porosity in clay J 2, at different 
temperatures. 



PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 81 





TRANS 


AM. CER SOC 


VOL 


X 






PURDV 


AMD MOORE. 


Plate: xlh 


16 






















23 






p^ 


r 


- 




■^ 












2* 

t i 

22 
> 

h 

a 
o 








— 


— 








k. 






















\ 


^ 




























o 



























Id 

a 
<n 












































!■•> 






















\c 










1 


J 


2 


— 








































R 


ATTLER LC 


)SS IT \A 


^ 












L* 























OlO oa Otj 04 O? I J i> 7 9 II 

TFtVlPERA-TuRrS EXPRET.SED IN CONES 

Curve showing changes In specific gravity of clay J 2, at different 

temperatures. 



82 PYRO-OHEMICAL, AND PHYSICAL, BEHAVIOB OF CLAYS. 



TRANS AVl CZ.R SOC VOL IX 



PURDV AND tv.CORt. P'-^TC: XUMI 































i 












1 ! 




! 

1 








1 i 












1 ! 










i 1 i i 






1 


1 : ! 










t 










i 












1 




1 














[ — ^ 


^^ 
















X 






n ^ 






i 




X 










! 




\ 










1 




1 \ 




i 
i I 






















I 1 ''"^—1''^ 


\ i i 








1 




\ 










1 




\ 










i 




\ 










! 




n 


\ 








R2 

AVING BRICK SrtAL 
*.TTi.ER uCSS ITS 


\ 






1 F 


E 


\ 










i 1 " 


\ 


1 






1 


^ 






! 






V 










1 1 • 




^ 














1 1 



010 Oe 06 04- 02 I 3 5 

TEr-IPERATURES EXPRESSED iN CONE: 



Curve showing changes in porosity of clay R 2, at different 
temperatures. 



PYKO-CHEMICAIi AND PHYSICAL BEHAVIOR OK CI.AVS. 83 



TRAN3 AM CtR SOC VOL IX 



PURDY AND MOORE. PU^-TE XUIV 



( 






















3 






^^ 


--- 


^ 


k 




















\ 


V 








i 














N 


V 






















\ 






















\ 
























\ 






















\ 


» 








































































R2 

PAVIN6 BRICK SHALE 
RATT1.CR LOSS IT 80 




































A 























TEMPERATURES. EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay R 2, at various. 

temperatures. 



p. ft M.-6 



84 



PYRO-CHEMICAL AND PHY8ICAL BEHAVIOR OF CLAYS. 





TRANS 


. AM. CER. SOC 


. VOL. IX 






PUKDV 


AND MOORc. PLATE KLV 










































































































































V 


















,1 


l^^^^^* 






N 






















^ 


< 






















\ 






















N 


i 






















V 






















\ 






















\ 














20 








^ 


^ 


L 




















\ 






















\ 






















\ 






















\ 










10 












\ 
























\ 














PAVIN6 BRICK SHALE 

RATTUER LOSS IS. II 


\ 










> 


L 


















V 






^ 






























X 


1 






o 























>o c 


« o 


« 




^ 


2 






3 


5 


7 


i t 



TEMPERATURES. EKPRESSED IN CONE3 

Curve showing changes in porosity of clay K 4, at different 
temperatures. 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS, 86 





TRANS 


AM CER &OC VOL IX 






PURDV AND MDORE, PLATE XLVt 














\^ 










2.6 

2* 

23 

22 
> 














\ 




















^ 


k 




















\ 






















\ 




















\ 


V 




















\ 




IL 

111 


















\ 










































































lb 




K4. 

PAVING BRICK SHALE 


































<* 


» 





















TEMPERATL/RES, EXPRESSED IN CONES 

Curve showing changes in specific gravity of clay K 4, at different 

temperatures. 



86 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 





TPAKJS 


•AM CCR 50C VOL 'X 






PU 


RDV AND MO 


ORE PL 


^TE XLVI 


























































































«« 
























































































'^, 




















u 


r 


^ 


\ 




















N^ 


















z. 






N. 
















3- 

a: 






> 


k 




















\ 














so 
>■ 








N 


































8 












\ 










o 

0. 












\ 






















\ 










10 








. 




\ 
























\ 


<v 












Fl 

PAVING BRICK 5HALE 
BATTUER LOSS ZOO'*- 


\ 












\ 






























































o 























Tf-^FERATURES ETXPRESSED IN CONE.^ 



Curve showing changes in porosity of clay F 1, at different 
temperatures. 



PYBO-CHBMICAL AND PHYSIOAIi BEHAVIOR OF CLAYS. 87 



^■' 


TRANS 


AM CER SOC. 


VOL 


IX 






PURDY 


AND MOORE 


PLATE XLVIIt 






















< 

26 











-j 


k 












a4 






1 







\ 


X 









12 

> 

> , 














-^ 


> 































o 
























IS 
































- 


F 


1 


— 












































BATTLER 1 


.esa COS 


pj 












!♦ 























TEMPERATURES, EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay F 1, at different 

temperatures. 



88 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 



TRANS. AM CER SOC. VOL," »>C 



PURDY AND 'MOORE. PLAXEXLIX 

























































































































































































' ^ 


k 




















\ 




















N 


L 




















^1 






















'^'"^ 


^^\ 




















^ 


\ 




















\ 




















\ 




















\ 




















\ 




















\ 
























1 










KI4- 

PAVING BRICK SHALE 
RATTLER LOSS 21 24- 


\ 










y 


V 
















X 
































N 


> 
























OtO c 


8 


6 C 


* 


C 


2 




3 




i 


7 


i I 



TEMPERATURES, EKPRESSEO IN CONES 



Curve showing changes in porosity in clay K 14, at different 
temperatures. 



PYBO-CHEMICAL AND PHYSICAL, BEHAVIOR OF CLAYS. 89 



TRANS 


AM CER SOC 


k/OL IX 






PUROV 


AND. MOORE. PLATE L 














































\ 














\ 






i 














\ 






















\ 




















N 


) 














































































































K14 

PAVIN6 BRICK SHALE 
RATTLER L^aS 21. ai 





















































CIO oe ot o 0^ I J s 

TEMPERATURE5. EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay K 14, at different 

temperatures. 



90 



PYRO-CHEMICAL AND PHYSIOAL BEHAVIOR OF CLAYS. 





TPANS. AM CER SOC 


VOt-. IX 








PUBOV 


AND MOORE P> 


-ATE LI 
























































































*0 


























































































rx 






















> 


I 
















Q. JO 

a) 

a. 






\ 
















z 






\ 
















Q 

(0 






\ 
















in 
u 






\ 
















X 

20 

> 

H 






V 


1^ 


X 




















\ 






















\ 










o 
a 
o 












\ 
















. 






\ 






















\ 


























^ 


) 












S I 

PAVING BRVCK SHALE 
Rattier loss C6 23 










































































o 























I 



TEMPERATURES. EXPRESSED IN CONES 



Curve showing changes in porosity in clay S 1, at different 
temperatures. 



PYKOCHRjrtOAT, AND PHYSIOAIi BEHAVIOR OF CLAYS. 91 



tt 


TRANS 


. AM CER SOC 


VOL IX 






PUROY 


AND MOORE. PLATE LH 






















< 


























"\ 


= 


hN 












23 
> 

q: 


o 












\ 






















) 
















































o 
y 
a. 

19 
18 


























































































< 


5 1 

PAVING BRICK SHALE 
RATTcEB I.033 ee. 33 




































4 


» 





















TEMPERATURES. EXPRESSED IN CONES 

Curve showing changes in specific gravity of clay S 1, at different 

temperatures. 



92 



PYKO-CHEMICAL AND PHYSICAL BEHAVIOR OP CLAYS. 



The chemical composition of the above clays are as 
follows :^ 



Sam. 
No. 


Mois- 
ture 


Vol'til' 
matter 


SiO, 


Al^Oj 


fe.O, 


CaO 


MgO 


KNaO 


FeO 


TiO, 


R 3 


1.06 


5.95 


58.57 


20.40 


7.40 


0.63 


1.37 


3.27 






R 2 


1.29 


4.86 


63.41 


18.61 


5.82 


0.41 


1.16 


3.60 






J II 


1.98 


6.76 


62.70 


16.95 


8.98 


1.19 


1.47 


3.03 






F 1 


2.02 


7.72 


58.52 


15.67 


4.99 


1.05 


1.45 


4.42 


3.37 


0.96 


K 1 


0.48 


6.99 


63.36 


15.43 


1.80 


0.93 


1.58 


3.84 


4.02 


i.oa 


K 4 


0.51 


5.47 


64.09 


14.16 


2.65 


1.69 


1.64 


3.67 


3.16 


0.89 


K 6 


0.38 


5.88 


63.62 


16.28 


3.02 


0.63 


1.44 


3.10 


2.90 


0.96 


K 3 


0.29 


7.89 


59.34 


15.36 


3.26 


0.76 


1.82 


4.62 


3.84 


1.31 


K 14 


0.51 


6.47 


64.09 


14.16 


2.65 


1.69 


1.64 


3.67 


3.16 


0.89 



Calculated into molecular ratios, the above analyses 
reduce to : 



Sample 1 
Number | 


CaO 


MgO 


KNaO 


Fe,0, 


AljOj 


SiO, 


FeO 1 


TiO„ 


R 3 


0.056 


0.171 


0.209 


0.231 


1.00 


4.88 






R 2 


0.040 


0.159 


0.253 


0.199 


1.00 


5.79 







J II 


0.125 


0.221 


0.234 


0.378 


1.00 


6.29 






F 1 


0.122 


0.236 


0.359 


0.203 


1.00 


6.35 


0.305 


0.078 


K 1 


0.110 


0.261 


0.290 


0.074 


1.00 


6.98 


0.369 


'0 . 083 


K 4 


0.042 


0.282 


0.277 


0.181 


1.00 


5.78 


■0.156 


0.060 


K 6 


0.070 


0.225 


0.325 


0.118 


1.00 


6.64 


0.252 


0.075 


K 3 


0.090 


0.302 


0.356 


0.135 


1.00 


6.57 


0.354 


0.108 


K 14 


0.217 


0.295 


0.311 


0.119 


1.00 


7.69 


0.309 


0.080 



The mechanical analyses^ of the above clays are as fol- 
lows: 



Sample 
Number 


L'gerthan 
1 m. m. 


m. m. 


0.1-0.01 
m. m. 


01-0.001 
m m. 


0.001-0 
m. m. 


Total 


Surface fac- 
tor by Pur- 
dy's method 


R 3 


11.695 


6.302 


52.902 


21.605 


11.791 


104.295 


290.67 


K 1 


7.276 


6.534 


56.078 


24.861 


9.766 


104.515 


256.476 


K 4 


1.402 


1.744 


48.875 


29.416 


22.242 


103.68 


513.508 


K 6 


1.241 


1.832 


65.836 


25.984 


7.772 


102.666 


220.596 


K 3 


1.500 


2.413 


57.155 


25.148 


13.968 


100.18 


341.155 


K 14 


H.331 


6.311 


42.751 


25.035 


9.672 


98.999 


254.354 



•Analyses by Professor S. W. Parr, University of Illinois. 
»By J. F. Krehbiel and J. K. Moore. 



PYKO-CHEMICAL AND PHYSICAL BEHAVIOR OP CLAYS. 



93 



The rattler losses as determined on the commercial 
product of these clays,^ obtained direct from the factories, 
are given in the following table, b, c. d. and e. signify re- 
spectively, Soft-burned, No. 2 or "Alley" grade, No. 1 
Paver, and Over-burned. 



Sample 
Number 




Total Rattler Loss 
at end of 




Absorption 
in per cent 

1 


Tranverse 
Modulus 
ot Rupture 




600 
Revolu. 


1200 
Revolu 1 


1800 
Revolu. 




R 3 


8.74 


12.22 


14.80 




1.27 


2800 


R 2 


9.76 


14.78 


18.61 





2.21 


2505 




450 


900 


1350 


1800 






Revolu. 


Revolu. 1 Revolu. |' Revolu. | 


2.315 




J II 


8.43 


12.25 


15.11 


17.14 


2220 


Fib 


19.32 


29.31 


38.88 


46.67 


13.2 




c 


12.70 


19.81 


25.08 


30.15 


4.8 


1700 


' d 


9.13 


13.89 


17.64 


20.84 


2.8 


1980 


e 


9.75 


17.20 


23.22 


28.35 


1.7 


1670 


K 1 b 


17.37 


28.56 


39.96 


46.06 


11.2 




c 


13.28 


21.46 


28.20 


33.91 


6.1 


1630 


(1 


8.43 


11.50 


14.08 


15.82 


0.9 


2535 


e 


9.42 


16.15 


21.77 


26.99 


1.2 


1420 


K 4 b 


19.69 


30.60 


38.17 


45.12 


12.20 


980 


c 


9.22 


14.47 


17.00 


19.94 


5. '00 


2360 


d 


9.91 


14.18 


16.87 


19.11 


1.16 


2250 


e 


14.83 


18.92 


broh 


en up 


0.60 


1890 


K 6 b 


7.9 


13.36 


18.20 


22.77 






c 


7.5 


11.68 


15.40 


18.33 






d 


5.84 


9.06 


11.58 


13.25 






e 


8.42 


12.85 


16.52 


20.32 






K 3 b 


18.54 


29.53 


38.35 


46.21 


10.0 


995 


c 


11.34 


17.45 


21.23 


24.61 


3.5 


2100 


d 


12.69 


19.01 


22.49 


24.89 


1.05 


2350 


e 


11.07 


18.58 


23.11 


26.42 


0.70 


2700 


K 14 d 


8.35 


13.35 


17.30 


20.79 


4.218 


1617 



'By Professor A. N. Talbot, University of Illinois. 



94 



PYRO-CHEMICAIi AND PHYSICAL BEHAVIOR OF CLAYS. 



The writers confess their inability to correlate the 
chemical and mechanical analyses of these clays with their 
pyro-chemical behavior or their rattler loss, but since 
they represent the most commonly accepted facts which 
have been collected heretofore in the study of paving brick 
clays, they are here recorded for reference. 



PYBO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 95 

COMMON OK HUILUING BRICK SHALES. 

Typical porosity aucl speeilic gravity curves of this 
class of clays are given in the following six charts. 

The striking difference between these and the paving 
brick shales is apparent. Earlier vitrification, irregularity 
in decrease of porosity and specific gravity, apparently 
larger quantity of vesicular glass formed within the mass, 
or at least a more notable bloating, due to volatilization of 
certain constituents, probably the soluble and adsorbed 
salts, are the distinguishing features of this class. 

Sufficient evidence is at hand to warrant the state- 
ment that any clay which vitrifies to a porosity of 2 or 3 
per cent, before cone 5 is reached in the heat-treatment pre- 
scribed in this method of burning test pieces, will be too 
brittle for use as paving brick material, no matter how 
little vesicular structure is developed. The fact is, how- 
ever, that it will be a rare case in which vesicular struc- 
ture is not strongly developed, if the clay shows an early 
and rapid rate of vitrification. 

The use of the comparative terms "early" and "rapid" 
in reference to this type of clays in contrast to their rela- 
tive use in regard to fire clays, is best illustrated by refer- 
ence to the curves. 

While the writers admit that the evidence here pre- 
sented is too meagre to permit of a complete or satisfactory 
plan of classification, they do feel that it is sufficient to 
indicate that a classification on the basis suggested is more 
rational than any other heretofore presented. 



96 



PYRO-CHBMICAL AND PHYSICAL BEHAVIOR OP CLAYS. 





TRANS 


AM CER SOC 


VOL IX 








PURDY 


AND MOORE. PLATE Ull 




























































































































































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\ 




















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FS 

COMMON BRtCK SHALE 










\ 






















L^ 


































p 


































TEMPERATURES. EXPRESSED IN CONES 

Curve showing changes in porosity of clay F 8, at different 
temperatures. 



1 



PYKO-CHEMICAL AND PHYSICAIi BEHAVIOR OF CIiAY8. 97 





TRANS 


AM. CER SOC 


VOL 


IX 






PURDY 


AND MOORE, PLATE UIV 


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COMMON BRICK SHALE 




































t4- 























O>0 OS 06 O*^ 02 I 3 i 

TEMPERATURES. EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay F 8, at different 

temperatures. 



98 



PYRO-CHEMICAIi AND PHYSICAL BEVAVIOR OF CLAYS 





TRANS 


AM CER SOC 


VOL. rx 








PURDV 


/AND MOORE PLATE LV 
















































































































































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Curve showing changes in porosity of clay F 9, at different 
temperatures. 



PYRO-CHEMICAL AND PHYSICAL. BEHAVIOR OF CLAYS. 99 





TRANS. 


AM CER. SOC 


VOL. IX 






PURDY AND MOORE. PLATE UVI 


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1 












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TEMPERATURES. EXPRESSED IN CO:Jf:; 



Curve showing changes In specific gravity of clay F 9, at different 

temperatures. 



100 



PYRO-CHEMICAL AND PHY8I0AI. BEHAVIOR OF CLAYS. 



TRANS AM. CER SOC VOL IX 



PURDY AND MOORE. PLATE. LVII 



































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COMMON BRICK SHALE 






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TEMPERATURES. EXPRESSED IN CONeS. 



Curve showing changes in porosity of clay No. F 10, at different 
temperatures. 



PYBO-CHBMIOAL AND PHYSICAL BEHAVIOR OF CLAY8. 101 





TRANS 


AM CER 


SOC VOL IX 








PUROV 


».ND_'M0OREJ PLATt LVIII 






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OlO 06 Ofc CM- 02 I 

TCMPERATURES. EXPRESSED IN CONES 



Curve showing changes in specific gravity of clay F 10, at different 

temperatures. 



p. & M— 7. 



102 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 



COMPARATIVE THERMO-PHYSICAL CHANGES. 

The following curves are presented to show the com- 
parative rate at which the three most important thermo- 
physical changes take place. 

A full explanation of the method of plotting these 
curves has been given earlier in the text. 

The volume, porosity, and specific gravity of the dry 
unfired brick being considered as a basis, and plotted in 
the datum line, the co-ordinate points of increase or de- 
crease of these same factors in the burned brick are plotted 
as shown on the curves. 



PYRO-CHEMICAL AND PHYSICAL BKHAVIOR OF CLAYS. 



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PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 



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PYRO-CHBMICAL. AND PHYSICAL BEHAVIOR OF CLAYS. 



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PYRO CHEMICAIv AND PHYSICAL BEHAVIOR OF CLAYS. 



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PYRO-CHHMICAL AND PHYSICAL BEHAVIOR OF CLAY8. 



109 







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110 PYRO-OHEMICAL AND PHYSICAL BEHAVIOR OP CLAYS. 

ULTIMATE FUSIBILITY OF CLAYS. 

Liidwig-,^ by the application of kiiown i^liysico-cheiiii- 
cal laws, deduced a scheme by which he was able to predict 
the fusibility of clays. H. J. Robertsoii,^ discussing Lud- 
wig's results quite fully, concurred in his general conclu- 
sions. The Ludwig scheme as presented by Robertson was 
followed in the construction of the chart on page 313. 

The Seger cone molecular formulae were reduced to 
Al203=l. The molecular equivalents of silica were plotted 
on the ordinate, and the molecular equivalents of RO fluxes 
on the abscissae. It will be noted that in no case does the 
molecular ratio of AI2O3 to SiOa exceed 1 :10. This being 
the ratio of AI2O3 to SiOg in cones 5-25, their co-ordinate 
position is located on a horizontal line drawn from the or- 
dinate 10. Having the chemical composition of clays of 
various kinds, the chart was prepared and the co-ordinate 
position of each clay plotted. 

The accuracy with which the fusibility of a clay can 
be thus ascertained, is shown by the fact that in nearly 
every case, the result reached by plotting the molecular 
ratios checked with that reached by the actual fusibility 
test, regardless of the purity or grade of the clay tested. 

The labor of making the analyses and calculating the 
molecular formulae, and the chances of disagreement be- 
tween the plotted and actual fusibility, places the Ludwig 
scheme at a serious disadvantage. Inasmuch as direct 
tests afford an easier and surer method, Ludwig's indirect 
test will hardly come into general use. The Ludwig scheme, 
however, has been of great value in that it has established 
the fact that clays, although a heterogeneous mixture of 
minerals, do, as a rule, obey definite laws in fusion. 



^Tonindustrie Zeitung No. 63, 1904, abstracted by Prof. Bleininger, 
Vol. VII, p. 275, A. C. S. Trans. 

'Brick, Vol. XXV. No. 2, 1906, p. 62. 



PYRO-CHEMICAL, AND PHYSICAL BEHAVIOR OF CLAYS. 



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112 PYRO-OHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 

CONCLUSIONS. 

The writers have attempted to indicate the thermp- 
chemical and physical changes that take place in the burn- 
ing of clay wares. Some effort has been made to show the 
causes of the various phenomena noted, but in the main, 
because of the lack of data, they have been reluctant to 
advance explanations with any degree of positiveness. It 
is believed, however, that by means of the method of study 
here presented, the following facts in regard to a clay can 
be established : 

1st. Exact industrial possibilities. 

2nd. Factor of safety to (a) vitrification range, (b) 
fusion range, (c) deformation. 

3rd. That while thermo-chemical and physical 
changes follow definite laws, they cannot be foretold by 
any analysis of the primary causes (physical properties of 
the unlired clay) now known. 

In conclusion, the writers desire to express their ap- 
preciation of the kindness of Dr. H. Foster Bain, Director 
of the State Geological Survey of Illinois, in permitting 
the use of considerable data collected by the Survey, and 
also of Professor C. W. Rolfe, Director of the Ceramic De- 
partment of the University of Illinois, and the University 
officials, in liberally supporting the researches that made 
this presentation possible. 

The chemical analyses given in this paper were made by Mr. David 
Kline and Dean Burns under the direction of Prof. S. W. Parr. 

DISCUSSION.* 

Mr. Yates: Were these various tests burned under 
the same conditions — that is, was the temperature of the 
kiln uniform? 

Mr. Moore : These clays were placed all in the same 
kiln, at the same time, in saggars, and were burned in the 



*Thls paper was not read in Its entirety, but was abstracted and presented in connec- 
tion with the curves by Mr. Moore. Some ot the discussion would probably not have taken 
place had the paper been read in (uU. 



PYRO-CHEMICAL, AND PHYSICAL BEHAVIOR OF CLAYS. 113 

same operation. Our kiln melts the same cone at the top 
as at the bottom, so it is certain that we get a uniform dis- 
tribution of heat. 

Mr. Yates : That being the case, isn't your conclusion 
that the common brick shale, whose curve fell so quickly, 
is not suitable for paving brick purposes unwarranted? 
Under the same conditions of firing, these common brick 
shales would not stand the temperature, but if fired slower, 
how do you know that they might not have made as good 
or tougher brick than the shales whose curves descend 
more gradually. 

Mr. Purdy: Mr. Moore has covered the ground, I be- 
lieve, in a thorough manner ; but I wish to bring out a little 
more emphatically the difference between the No. 1 and 
No. 2 fireclays. The No. 1 fireclays, (indicating plates IX- 
XVIII) you will notice, vitrify very slowly. The No. 2 
fireclays have an early vitrification, but from there on, 
they have a very slow fusion rate. They vitrify under 
stoneware or facebrick heat- treatment, and could be used 
for either of those purposes. But their actual fusion 
points agree closely with those of the No. 1 fireclays, and 
the chemical analysis also agrees in many ways with that 
of the No. 1 fireclays. The only means of differentiation 
is in the plotting of their vitrification phenomena in these 
curves, and noting the remarkable variation which they 
show. In the case of what we have called No. 3 fireclays, 
the vitrification is not only more rapid, but the actual 
fusion point is also considerably lower. A paper was read 
by Mr. Bleininger on physical chemistry yesterday, and I 
noted halts in his curves, as shown in these. There is a 
problem there, for the physical chemists to solve. I feel 
assured that when they can give an explanation for that 
halting in the porosity curve (and the same is noted in the 
specific gravity curve), it will throw a great light on our 
methods of determining the possible value of the clay. 
This work which we are presenting in this paper is, per- 
haps, a crude introduction to the chemical-physical method 
of studying our most common clay working operations. 



114 PYRO-CHEMICAL AND PHYSICAL. BEHAVIOR OF CLAYS. 

In the description of the microscopic slides Mr. Wege- 
mann stated that the iron had not discolored the glass, 
until after cone nine had been reached. That is equivalent 
to saying that the iron had not operated as a flux, even at 
cone nine. We have many of us been of the opinion that 
iron was one of the most active fluxes in the scale, and we 
are not yet readj^ to give up that opinion ; but by examina- 
tion of the specific gravity curves and microscopic slides, 
we must admit that the iron seems not to enter into active 
fluxing action. At any rate, the glass did not take the iron 
into solution and the iron had not probably fluxed the clay 
particles to any great extent, for the glass would take it up 
before the clay particles would. 

I would like to call your attention to the rattler losses 
placed on the plates of the paving brick shales, numbers 35 
to 52. Observe plate XXXV showing a rattler loss of 13.25 
and plate LI showing 26.23. Observe the relative changes 
in porosity and specific gravity in conjunction with the 
rattler loss. Mr. Moore emphasized the fact that this de- 
crease in specific gravity was due to the formation of glass. 
We know that when a glass is first formed, whether in the 
glass pot or in glazes, that there is a boiling up or evolution 
of gas. This is especially noticeable when burned rapidly. 
When burned slowly, the glass is not boiled up so much, 
but is still vesicular in structure ; that is, it contains small 
blibs or sealed cavities into which water from the outside 
could not penetrate. 

In Plates LIX to LXV, the datum line represents the 
measurements obtained on the unburnt clay. The figures 
above show the increase of porosity or specific gravity or 
volume over these properties of the raw clay, and the fig- 
ures below that datum line show the decrease of these same 
properties below that of the raw clay. Thus we see that 
samples drawn at cone 010 generally showed actually 
greater porosity, greater real specific gravity and greater 
volume than the raw material showed, while samples 
drawn at higher temperatures showed these properties, one 
or all, to be about the same as the initial measurements 



PYRO-CHEMICAL AND PHYSICAL BEHAVIOK OF CLAYS. 116 

and still higher temperatures showed marked falling ofif in 
all three sets of properties. I do not pretend to understand 
all the phenomena brought to light in this study, for I have 
not yet had the assistance of one well grounded in physical 
chemistry. 

In the plates LIII to LVIII, are shown brick made of 
common shale. There have been engineers who have in- 
sisted on the specific gravity test, as a test of the wearing 
qualities of paving brick. We have found that when the 
true specific gravity, that is, the specific gravity of the 
mass as a whole, is taken, it gives a good index of the 
strength of the product. This is well shown in these charts. 
The specific gravity cannot be taken direct : It must be 
taken in connection with the specific gravity of the raw 
clay, in order to get a comparison between the two. What 
does the specific gravity tell you? It tells you the extent 
to which this glass matrix, which Mr. Wegemann has de- 
scribed, has become blibbed or foamy. The more foamy it 
has become, the weaker your clay will be and the heavier 
will be its rattler losses. 

Mr. Yates: Do I understand that these globules of 
glass are separate particles in the body of the brick, or are 
they assimilated with the body of the brick? 

Mr. Purdy: A study of all the clays in microscopic 
section shows similar phenomena. There will be a particle 
of quartz, a particle of some other amorphous substance, a 
particle of fused glass, you might say, in a row, like the 
cross section of a sausage, mixed hit or miss. There is no 
regularity about it; it is not stratified. 

Mr. Binns : I want to ask Mr. Purdy, in connection 
with that iron fusion, where the hematite crystals are seen 
appearing, isn't what followed evidence of combination of 
the iron with the silica? 

Mr. Purdy: No. 

Mr. Binns: Was it reduced? 

Mr. Purdy : Yes, but in many instances the hematite 
crystals were formed even where there was every appear- 



116 PYRO-CHEMICAL AND PHYSICAL BEHAVIOR OF CLAYS. 

ance of wholly reducing conditions. The increase of hema- 
tite crystals progressed through the red or ferric state into 
the black or ferrous brick. 

I want to draw attention to the fact that some of these 
fireclays had so little flux that it was not noted in the 
chemical analysis, the alumina, silica, titanium, and water 
being the only constituents reported. What is there in 
such a clay which forms this gla«s? What is it in the 
shales? There is a nice little problem in your adsorption 
theory. We are beginning to put two and two together, 
but we are not quite yet willing to add them. 



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